Fastest marine rail tunnel The 10.8 km-long Shiziyang tunnel crossing the Pearl River estuary in south China's Guangdong province is designed for trains travelling at 350 km/h. Apart from being the longest tunnel in China, it will also be the fastest underwater tunnel in the world. It is part of a 140 km-long high-speed rail link between Guangzhou, the capital of Guangdong, with Shenzhen and Hong Kong. Construction of the tunnel, 60 m below surface, started in November, 2007 using four NFM TBMs with PPS guidance and the first tube has already holed. The rail link will be commissioned in 2012, reducing travel time between Guangzhou and Hong Kong to 40 min from the current 120 min. It will join the China express railway network, which will ultimately reduce travel time between Hong Kong and Beijing to 8 h. 12/11.