Chinese workers excavates an underwater railway tunnel near the estuary of the Pearl River at Shiziyang, near the Humen Bridge, south China, November 13, 2007. Nov. 14 - More than 300 Chinese workers have begun excavating an underwater railway tunnel near the estuary of the Pearl River, in south China.The structure will be China's first underwater rail tunnel and also the country's longest underwater tunnel of any kind, according to Guo Dahuan, chairman of the board of China Railway Tunnel Group, builder of the project.According to Guo, the tunnel is a key part of a 146-km express rail link that will connect Guangzhou, the capital of Guangdong Province, an economic powerhouse of China, with Shenzhen City, also in Guangdong, and Hong Kong.The project, with a length of 10.8 kilometers, will cross the Pearl River estuary at Shiziyang, near the Humen Bridge, to link Guangzhou, situated on the Pearl River, and Dongguan, located in the southeast of Guangzhou.Four large shielding machines are being used to dig the tunnel, which is to be finished in April 2009. The budget for the project is 2.4 billion yuan (about 300 million U.S. dollars).The Guangzhou-Shenzhen-Hong Kong express, with trains traveling at 350 kilometers per hour, is scheduled to begin service in 2010.The express will enable visitors to travel among the three locations within one hour.