While in Brazil the São Paulo-Rio high-speed train never materialized, China plans to tunnel 120 km under the sea to connect two cities by rail — 90 km will be underwater, with trains at 250 km/h, and the 8-hour journey will be reduced to 40 minutes.

Written by Douglas Avila

Published on 23/04/2026 at 00:31

Updated 23/04/2026 at 00:32

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While in Brazil the high-speed train between São Paulo and Rio has never left the drawing board, China plans to drill 120 km under the sea to connect two cities by rail — 90 km will be underwater, trains will travel at 250 km/h and the journey that currently takes 8 hours will be reduced to 40 minutes

There is a narrow strait of water in northeastern China that separates two giant industrial regions. To cross the Bohai Strait today, passengers need a ferry that takes 8 hours — when the weather allows.

China wants to solve this by drilling 120 kilometers of tunnel under the seabed, creating the largest underwater railway tunnel in history.

The Bohai Strait Tunnel project would connect the cities of Dalian, in Liaoning province, and Yantai, in Shandong province. With high-speed trains traveling over 250 km/h, the 8-hour journey would drop to just 40 minutes.

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90 km underwater — more than double the Eurotunnel

To understand the scale of this project, it must be compared to what exists.

The Eurotunnel, which connects England to France under the English Channel, has a total length of 50.5 km and 37.9 km underwater. It was inaugurated in 1994 and is considered one of the greatest engineering feats of the 20th century.

The Seikan Tunnel in Japan is 53.85 km long with 23.3 km underwater. It was the longest in the world until the Eurotunnel.

The Bohai Tunnel would have a total length of 123 to 125 km, with 90 km directly under the seabed. This is more than the sum of the underwater sections of the Eurotunnel and Seikan combined.

Eurotunnel: 37.9 km underwater, trains at 160 km/h
Seikan (Japan): 23.3 km underwater, trains at 260 km/h
Bohai (proposed): 90 km underwater, trains at 250+ km/h

There would be two parallel pipes excavated under the seabed, designed to transport passengers and vehicles — cars would be loaded onto railway cars, as is done in the Eurotunnel.

Between $28 and $43 billion — and China considers it “reasonable”

The estimated cost of the project ranges from $28 billion to $43 billion, depending on the source and final configuration.

In Brazilian reais, this would represent something between R$ 155 billion and R$ 238 billion.

For comparison, the Brazilian high-speed train between São Paulo and Rio de Janeiro — with a length of 510 km and WITHOUT an underwater tunnel — was budgeted at R$ 35 billion in 2010 and has never left the drawing board.

Chinese planners consider the investment “reasonable” given the expected economic benefits: integration of two industrial regions, reduction of logistics costs, and relief of the overloaded railway networks of Beijing and Tianjin.

The biggest challenge: drilling through one of the most active seismic faults in Asia

The engineering of the Bohai Tunnel faces an obstacle that no underwater tunnel in the world has had to overcome.

The route passes directly over the Tan-Lu Fault, one of the most active tectonic faults in all of East Asia.

Building 90 km of tunnel underwater in an active seismic zone requires special drilling machines — the so-called High-Performance Slurry TBMs — capable of operating under extreme hydrostatic pressures.

Advanced sensors, watertight compartments, and state-of-the-art construction techniques will be necessary to ensure that the tunnel withstands earthquakes without compromising passenger safety.

It is a challenge that no country has faced before on this scale.

100 million people connected by rail

The Bohai Strait separates the industrial northeast of China from the economic hub of Shandong.

The Bohai Circle Economic Zone is home to over 100 million people in one of the most densely industrialized regions on the planet.

Today, goods and people must detour the entire gulf by land — a journey of over 1,500 km — or wait hours for the ferry.

The tunnel would eliminate this logistical bottleneck, reducing what economists call the “Weighted Average Transport Cost” in northern counties that are currently isolated from economic centers.

The project is part of the Chinese 15th Five-Year Plan (2026-2030) railway strategy, which envisions high-speed networks in the “eight verticals and eight horizontals” format covering the entire country.

When the tunnel will be ready — and if it will really happen

The project was formally submitted to the National Development and Reform Commission of China in May 2019.

As of April 2026, it is still in the feasibility study, environmental assessment, and route definition phase.

If construction begins in the coming years, projections indicate 10 to 15 years of work — which would place completion between 2036 and 2041.

China has a track record of delivering megaprojects on time. The Dali-Ruili railway, which crossed 19 seismic faults and a 34 km tunnel, was completed in 14 years. The 16 km Jintang Tunnel under the sea is in its final stages.

But the Bohai would be of another magnitude. No country has ever built a 90 km tunnel under the ocean.

While Brazil debates, China drills

The comparison with Brazil is inevitable.

The São Paulo-Rio high-speed train project was launched in 2007. Nearly 20 years later, there is not a meter of track built.

China, in the same period, inaugurated over 40,000 kilometers of high-speed rail — the largest network in the world.

If the Bohai Tunnel is built, it will be the largest underwater engineering project in human history.

However, it is important to note that the project has not yet been officially approved. Estimated costs have already risen from $28 billion to $43 billion in different assessments, and the seismic challenges of the Tan-Lu Fault have no precedent in tunnel engineering.

The question is not whether China has the technical capacity to build it — it has proven that dozens of times. The question is whether the cost-benefit justifies drilling 90 km under the sea when land and bridge alternatives are also being evaluated.

Is it worth drilling to the bottom of the ocean to save 7 hours of travel? For China, apparently, yes.

If Brazil has not managed to build 510 km of high-speed train on the surface in 20 years, will we ever have the capacity — or the political will — to drill a tunnel under the sea?

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While in Brazil the São Paulo-Rio high-speed train never materialized, China plans to tunnel 120 km under the sea to connect two cities by rail — 90 km will be underwater, with trains at 250 km/h, and the 8-hour journey will be reduced to 40 minutes.

90 km underwater — more than double the Eurotunnel

Between $28 and $43 billion — and China considers it “reasonable”

The biggest challenge: drilling through one of the most active seismic faults in Asia

100 million people connected by rail

When the tunnel will be ready — and if it will really happen

While Brazil debates, China drills

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While in Brazil the São Paulo-Rio high-speed train never materialized, China plans to tunnel 120 km under the sea to connect two cities by rail — 90 km will be underwater, with trains at 250 km/h, and the 8-hour journey will be reduced to 40 minutes.

90 km underwater — more than double the Eurotunnel

Between $28 and $43 billion — and China considers it “reasonable”

The biggest challenge: drilling through one of the most active seismic faults in Asia

100 million people connected by rail

When the tunnel will be ready — and if it will really happen

While Brazil debates, China drills

While in Brazil a 10-story building takes 2 years to complete, in China a company stacks pre-fabricated modules and raises the entire building in just 28 hours and 45 minutes.

Egypt wants to draw 10 million cubic meters of water from the Nile per day into the desert, irrigate a new agricultural frontier, and build a city where there is currently only sand.

BRICS is preparing a payment system inspired by the Brazilian PIX that will allow direct transactions between countries using national digital currencies without relying on the dollar or Western banks as intermediaries.

Ethiopia has banned gasoline and diesel cars, placed over a hundred silent electric buses on the streets of Addis Ababa, and now aims for half a million electric vehicles by 2030, all powered by Africa’s largest dam and a courage that few countries have shown.

On the coast of China, fishermen received an official reward after finding 10 foreign underwater devices capable of “stealing secrets” in just two years, showing that the silent war for the seabed has already reached the nets of those who rely on fishing.

In the South Atlantic, three isolated volcanic islands cause the wind to draw perfect spirals visible from space: a rare phenomenon called von Kármán vortex streets forms symmetrical patterns behind the peaks of the South Sandwich Islands and was recorded by the NOAA-20 satellite in 2025.

Created to cling to ships like a lamprey, the new U.S. underwater drone sleeps on the ocean floor, launches torpedoes, and recharges itself with the current.

130 kilometers off the coast and with 260-meter-tall turbines, the world’s largest offshore wind farm is being assembled on the bottom of the North Sea — when complete, its 277 turbines will generate energy for 6 million homes in the United Kingdom.

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Scientists simulated what would happen if all of Earth’s oceans evaporated — and found the same mark on Mars, suggesting that one-third of the red planet was once covered by water.

The United States wants to extract minerals from the bottom of the Pacific at a depth of 4,000 meters — the problem is that 90% of the species living there are still unnamed, and in tests, life on the seabed decreased by 37%.

Climate change should be combated by solar and wind energy — but extreme heat reduces the efficiency of panels, violent winds shut down the turbines, and extreme rainfall floods entire power plants.

On the seabed near Singapore, divers found the country’s first ancient shipwreck — the 14th-century ship carried 3.8 tons of Chinese porcelain and the largest collection of Yuan Dynasty blue and white pieces ever recovered from a shipwreck.

130 kilometers off the coast and with 260-meter-tall turbines, the world’s largest offshore wind farm is being assembled on the bottom of the North Sea — when complete, its 277 turbines will generate energy for 6 million homes in the United Kingdom.