China will invest 260 billion yuan, or about $42 billion (27.7 billion pounds), 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 revenu...