China will invest 260 billion yuan ($42 billion) to revive a long-stalled plan to build the world's longest undersea tunnel across the Bohai Strait linking the country's eastern and northeastern regions, state media said on Thursday.

The 123-km (76.4-mile) tunnel will run from the port city of Dalian in northeastern Liaoning province to Yantai city in eastern Shandong, the China Economic Net website said.

The report did not say when the project will be completed.

China announced plans in 1994 to build the tunnel, at a cost of $10 billion, and set to be completed before 2010. But more than 20 years on, the project remains stuck in the planning stage, the website said, without elaborating.

At the time, state media said the tunnel would shorten the travelling distance between the two regions by 620 miles.

The costs could be recouped in 12 years, said Wang Mengshu, a member of the Chinese Academy of Engineering, who estimated annual revenues from the tunnel at around 20 billion yuan, the website said. "Freight is very profitable," Wang said.

The report comes nearly a month after Nicaraguan lawmakers gave a Chinese company a 50-year concession to design, build and manage a shipping channel across the Central American nation that would compete with the Panama Canal.

Japan has the world's longest undersea tunnel. The 54-km Seikan tunnel links Honshu and Hokkaido islands and started operating in 1988 after more than two decades of construction.

The Channel tunnel between England and France is about 51 km long. – Reuters