The world’s longest underwater high-speed rail project moves forward, aiming to link two continents beneath the sea

The first time you hear it, it sounds like science fiction: a train slipping beneath the sea, vanishing into the blue off one continent and emerging, hours later, on another. No airport queues. No turbulence over wild oceans. Just a humming carriage, soft overhead lights, and the rhythmic hush of steel moving through the dark. Somewhere above, whales migrate, storms roll over empty horizons, and the surface world keeps spinning. Down here, in a tunnel the length of a country, humanity would be trying something it has never done before: building the world’s longest underwater high-speed rail line.

A tunnel between worlds

Imagine standing on a platform at the edge of a continent, a cool salt breeze slipping in through the station doors every time they open. People wheel suitcases past racks of surfboards. Announcements echo off curved ceilings, the voice calm, almost casual, as if it isn’t about to send you under an ocean.

Now imagine that platform isn’t in Europe or Asia—those regions we usually associate with sprawling train networks—but part of a bold new line linking two continents beneath the sea. The project, still in its ambitious, carefully modelled phase, aims to dig a tunnel that would put every other undersea rail link to shame, stretching hundreds of kilometres through seafloor rock and sediment, carrying sleek high-speed trains at jet-like speeds.

For Australians, used to vast distances and long-haul flights, the idea lands differently. We live on an island continent that often feels like its own planet. To travel far, we fly. The ocean is something we stare at from clifftops, surf, fish, or sail across in days, not minutes. So the notion of a train journey that slips under that big, mythic blue and emerges on another landmass is almost dizzying. It upends what “far away” has always meant.

The engineering quiet beneath the waves

To build a tunnel like this is to choreograph a slow dance of machines and geology. Picture a tunnel-boring machine—TBM, in the dry terminology of engineers—as large as an office building, its rotating teeth chewing through rock that hasn’t seen daylight in tens of millions of years. Inside its metal shell, the air smells faintly of oil and metal; the sound is a constant grinding growl softened by layers of machinery and acoustic padding.

This isn’t just a single tube punched through the seabed. Designs for the world’s longest underwater rail tunnel juggle multiple bores: twin tracks for trains, emergency escape galleries, maintenance corridors, cable runs for power and communications. Pressure-proof doors. Ventilation systems that can clear smoke in minutes. Pumps standing by for the unthinkable: a breach.

We’ve done smaller versions of this before. The Channel Tunnel between Britain and France threads 50 kilometres under the English Channel. Undersea road tunnels connect Norway’s fjord-riddled coastlines. Yet what’s now on the table makes these look like practice runs. When planners talk about hundreds of kilometres under water, they’re talking about a structure so large, so long, that the Earth’s own curvature becomes part of the design. For a leg of that journey, there will be nothing above but water and sky, and nothing around but dense, silent rock.

Speed that bends the map

High-speed rail changes how we feel distance long before it changes the map. The first time you travel at 300 km/h on a quiet train, there’s a moment of disbelief. Trees flicker by like frames in an old film; distant hills appear and vanish. Yet inside, someone is calmly stirring sugar into a coffee, a child is tracing finger-smudged arcs on the window, another traveller is asleep, face pressed to the glass.

Now layer that familiar high-speed experience with the strange knowledge that you’re deep below an ocean. There are no lights outside, no passing towns, no highway ribbons. Just the porter walking through the carriage, the soft ding of the next stop announced, and a constant, low thrumming as tons of steel and electronics whisper along perfectly laid rails.

On routes already operating around the world, high-speed rail links have quietly stolen journeys away from planes. Two, three, four hours by train is, for many, preferable to the same time in airports and narrow seats at 11,000 metres. The underwater mega-tunnel promises similar logic: cut a multi-leg flight and days of logistics into a single, seamless journey. Board near a coastline; disembark in another country before your body has time to fully understand what just happened.

What this means when you live on an island continent

Australians know distance in our bones. We measure it in hours behind the wheel between coastal towns, in the yawning flight from Perth to Sydney, in the midnight haze of long-haul flights to Asia, Europe, or the Americas. We make jokes about “just up the road” meaning a four-hour drive. Our sense of isolation is wrapped into our humour, our politics, our culture.

So when a project on the other side of the world sets out to literally tunnel under an ocean, it reverberates here. It hints at a world where being “cut off” by sea is less absolute. Where oceans remain wild and free on the surface but are quietly woven beneath by lines of steel and electricity. While this particular project may not connect to our shores—at least not yet—it sets a precedent. It says, “This is possible.” And once something is proven possible, it has a way of eventually finding its way to every coastline on the globe, including ours.

There’s a thought experiment that keeps coming up in Australian transit circles: could we one day ride high-speed rail from a major eastern city to a port, then board an undersea line linking us into a transcontinental network? It’s not a promise; it’s barely even a plan. But it’s a horizon, and Australians, perhaps more than most, understand the pull of a far horizon.

Ocean, country, and consequence

Under all the sleek renderings and impressive speed estimates lies a harder question: what does carving a tunnel beneath the sea do to the world above it? Modern tunnelling is remarkably precise, far away from old ideas of blasting and chaos. Carefully mapped routes avoid fragile seabeds, underwater canyons, and sensitive habitats. Construction traffic is managed. Noise is modelled. Material excavated from the tunnel is handled, reused, or disposed of under strict controls.

But the ocean is not just a blank, blue ceiling. It’s whale song and migrating fish, currents thick with plankton, cold seeps where strange life gathers, ancient seabeds layered with the remnants of climates long gone. It’s also, increasingly, monitored and cherished by coastal communities, Indigenous custodians, and scientists who see its fragility written in coral bleaching and changing storm patterns.

Australians understand this tension. We are a people who adore convenience—same day delivery, on-demand everything—but we also live on a continent where the cost of careless development is written into the land: eroded coasts, salinised soils, rivers interrupted and remade. A project of this scale demands that we ask not just, “Can we do it?” but “How do we do it in a way that honours sea country?” That means environmental assessments shaped not only by numbers but by stories, by cultural knowledge, by voices that have been listening to ocean and land for tens of thousands of years.

Climate, carbon, and the slow turning of habits

There is, tucked inside this ambitious tunnel, a quieter story about climate. High-speed rail is often framed as a lower-emissions alternative to flying, especially over medium distances where aircraft currently dominate. Electricity—particularly when drawn from renewables—powers trains with a fraction of the carbon cost per passenger-kilometre of jet fuel.

Yet nothing about tunnelling under an ocean is carbon-light in the short term. Concrete, steel, heavy machinery, years of construction: all of it stacks up a substantial upfront footprint. The gamble is on the long view—that decades of often-full trains, displacing millions of flights, will balance and then outstrip that initial spike. To Australians watching from afar, the project becomes a kind of test case: can mega-infrastructure, done with a climate lens, genuinely help bend our emissions trajectory downward?

There’s also a cultural shift at play. Air travel has, for years, been the default fantasy of “getting away”—the soft click of the seatbelt, the lights dimming, the thrum of takeoff. High-speed rail asks us to rethink that narrative. Travel becomes less like a jump cut, more like a continuous shot: you depart, you move, you arrive, without the surreal time warp of airports. The underwater line adds another twist: your journey threads through a place you cannot see, a reminder that even our seemingly effortless motion leaves ripples in the dark.

The human scale inside a mega-project

When headlines describe the “world’s longest underwater high-speed rail project,” they tend to lean on numbers. Kilometres of tunnel. Billions in cost. Years until completion. It’s how we’ve learned to understand infrastructure: through scale, money, and political wrangling.

But the reality, once it opens, will be almost intimate. The smell of warm brakes as the train glides into a station. The low murmur of tired travellers. The gentle sway when the train slips from open-air track into the tunnel mouth and the world outside cuts sharply to black. Kids with their ears pressed to the walls just in case they can hear the ocean. Someone scrolling through photos of the city they just left, another flicking through a translation app for the city they’re headed toward.

For Australians—from FIFO workers used to red dust and propellers, to students who’ve grown up with budget airlines, to elders who remember when long-distance travel was still by sea—this is a different kind of dream to hold in the mind. We’ve long had our own big-vision rail conversations: fast lines between Brisbane, Sydney, Canberra, and Melbourne; inland freight corridors cracking the tyranny of distance. Watching the world’s longest underwater line take shape is like seeing a distant cousin attempt something wild and unprecedented. If they pull it off, the family stories change for everyone.

A glimpse of future routes from our shores

Stand on any busy Australian headland at dusk and you’ll see it: planes arcing overhead on invisible highways of air, their engines a faint roar against the slap and hiss of waves on rock. Beneath them, container ships ride the swell, stacked high with the physical stuff of global trade. Add to that picture, in your mind’s eye, another invisible line: a thread of steel buried in the seabed, carrying people at enormous speed from continent to continent.

We are not likely to see a Sydney–somewhere-undersea tunnel in the immediate future. Our distances are still too enormous, our population too stretched, the engineering challenges multiplied by plate boundaries and deep ocean trenches. But the story now unfolding elsewhere—the methodical planning, the debate over risk, the blend of daring and caution—will feed into our own long-term choices.

When Australian policymakers weigh new high-speed corridors, when coastal communities negotiate what kind of development they’ll allow at their doorstep, they will do so in a world where “tunnel under an ocean” is no longer shorthand for fantasy. It will be something another nation actually did, with lessons documented in seismology reports, biodiversity surveys, and stories from passengers who rode the line in its first quiet years.

There’s a certain humility in that. We are an island, yes, and proudly so. But we are also part of a planet that is restitching itself in steel and fibre, not to erase the sea, but to slip, respectfully and carefully, beneath it. And somewhere in that slow, careful stitching, Australia will have to decide what kind of threads it wants to add.

At a glance: The world’s longest underwater high-speed rail project

Frequently Asked Questions

Will this underwater high-speed rail line connect directly to Australia?

No. The project now moving forward is focused on linking two other continents, not Australia. Its importance for Australians lies in what it proves possible—technically, economically, and environmentally—and the way those lessons may influence future regional projects in our part of the world.

How safe is it to travel through a tunnel beneath the sea?

Modern undersea tunnels are built with multiple safety layers: thick linings, pressure-resistant structures, advanced monitoring, fire suppression systems, and dedicated evacuation passages. While any infrastructure carries some risk, safety is one of the most heavily regulated aspects of high-speed rail projects, particularly those under water.

Could this kind of project help reduce global emissions?

Potentially, yes. Once operating at scale and powered by low-carbon electricity, high-speed rail can emit far less CO₂ per passenger-kilometre than planes. However, the construction phase is carbon-intensive, so the long-term climate benefit depends on high usage, clean electricity, and careful design choices.

What might Australians gain from projects like this, even if they are overseas?

Australians gain experience indirectly: proven engineering methods, refined environmental standards, and clearer data on the economics of mega-projects. All of this can shape how we approach our own long-distance rail plans, coastal developments, and regional connections across the Indo-Pacific.

Is it realistic to imagine an underwater rail tunnel to or from Australia one day?

With today’s technology and economics, tunnelling all the way to Australia would be extraordinarily challenging. Our separation by deep oceans and vast distances makes it a very long-term idea. But the history of infrastructure is full of once-impossible projects becoming routine. As undersea tunnels grow longer and more sophisticated elsewhere, the range of what’s considered “realistic” will continue to shift.