The second tunneling boring machine that is to be used for constructing the world's longest undersea high-speed railway tunnel was unveiled in Changsha, Central China's Hunan province, on Monday.

The TBM, named Yongzhou, has an excavation diameter of 14.57 meters, a length of 135 meters and a total weight of 4,350 tonnes. A similarly sized machine, named Dinghai, was unveiled in early January.

The two machines will head-to-head excavate the Ningbo-Zhoushan Railway's tunnel linking Jintang town of Zhoushan in the east and Yinzhou district of Ningbo in the west in East China's Zhejiang province.

The Ningbo-Zhoushan Railway is about 77 kilometers long, with a designed speed of 250 kilometers per hour. The tunnel will be around 11 kilometers long.

According to the plan, Yongzhou will start from Ningbo, and Dinghai from Zhoushan. They will meet undersea and ensure accuracy that does not exceed 20 millimeters.