China is considering plans to build a high-speed railway line to the US, the country's official media reported on Thursday.

The proposed line would begin in north-east China and run up through Siberia, pass through a tunnel underneath the Pacific Ocean then cut through Alaska and Canada to reach the continental US, according to a report in the state-run Beijing Times newspaper.

Crossing the Bering Strait in between Russia and Alaska would require about 200km (125 miles) of undersea tunnel, the paper said, citing Wang Mengshu, a railway expert at the Chinese Academy of Engineering.

"Right now we're already in discussions. Russia has already been thinking about this for many years," Wang said.

The project – nicknamed the "China-Russia plus America line" – would run for 13,000km, about 3,000km further than the Trans-Siberian Railway. The entire trip would take two days, with the train travelling at an average of 350km/h (220mph).

The reported plans leave ample room for skepticism. No other Chinese railway experts have come out in support of the proposed project. Whether the government has consulted Russia, the US or Canada is also unclear. The Bering Strait tunnel alone would require an unprecedented feat of engineering – it would be the world's longest undersea tunnel – four times the length of the Channel Tunnel.

According to the state-run China Daily, the tunnel technology is "already in place" and will be used to build a high-speed railway between the south-east province of Fujian and Taiwan. "The project will be funded and constructed by China," it said. "The details of this project are yet to be finalised."

The Beijing Times listed the China-US line as one of four international high-speed rail projects currently in the works. The first is a line that would run from London via Paris, Berlin, Warsaw, Kiev and Moscow, where it would split into two routes, one of which would run to China through Kazakhstan and the other through eastern Siberia. The second line would begin in the far-western Chinese city of Urumqi and then run through Kazakhstan, Uzbekistan, Turkmenistan, Iran and Turkey to Germany. The third would begin in the south-western city of Kunming and end in Singapore. The routes are under various stages of planning and development, the paper said.