Shield tunneling began on the Suzhou East Tunnel high-speed railway project in East China on Thursday, marking a milestone in the construction of the country's longest urban high-speed railway tunnel, said China Railway's 14th Bureau Group, which is building the tunnel.

When completed, the tunnel, in Suzhou, Jiangsu province, will extend for 15.57 kilometers and be used by trains traveling at up to 350 kilometers per hour.

It is the highest standard and longest urban high-speed railway tunnel under construction in China.

The tunnel, next to Yangcheng Lake, will pass beneath three railways, two subways, four rivers and lakes, more than 20 important city roads and several buildings. It will be up to 58 meters underground and will have to bear a great deal of pressure said Qu Kejun, an engineer with the group.

"Our team has tailored a large-diameter shield tunneling machine for this project — the Tongyong Yuanmeng tunnel boring machine. It is domestically produced, and also one of the most intelligent tunnel boring machines in China," he said.

The machine, with a diameter of 14.81 meters, is about as tall as a five-story building. With a total length of 134 meters and weight of 4,200 metric tons, the machine has been specifically designed to adapt to ultra-long distances and resist pressure and corrosion, he said.

It uses several domestically developed cutting-edge technologies including advanced geological forecasting and automatic monitoring.

The tunnel will be part of a railway linking Nantong in Jiangsu and Ningbo in Zhejiang province, an important part of the coastal corridor of China's high-speed railway network. Upon completion, the new line will link with several operational high-speed railways including the Beijing-Shanghai High-Speed Railway and the Shanghai-Kunming High-Speed Railway. It will further improve the railway network in the Yangtze River Delta region, playing a crucial role in promoting the high-quality integrated development of the area.