XIAMEN -- A coastal Chinese city on Thursday started construction on a 6-billion-yuan ($949 million) undersea tunnel linking Xiamen's downtown island with its major industrial district.

The 9.03-km tunnel will link downtown Xiamen with Haicang District, the largest Taiwanese investment zone in the Chinese mainland in terms of size, when it is completed in 2016, local officials said. The bottom of the tunnel will be built 72.6 meters below the ocean surface.

Zhang Canmin, vice mayor of Xiamen, said the tunnel is key to building a network of highways to improve logistics in the economically robust region, which has been a focus of Taiwanese investment over the past three decades.

Xiamen was one of the first special economic zones China set up in the late 1970s and early 1980s to test market-oriented economic reforms. Business used to be centered in the city's downtown island but has gradually expanded to its mainland districts.

The Chinese mainland's first undersea tunnel, linking downtown Xiamen with the city's mainland Xiang'an District, opened to traffic in April 2010.