The world's largest shield machine for railway construction, a tunneling device with a diameter of 15.4 meters, reached the middle point of the tunnel's underwater section on April 16, marking a milestone in the construction of the tunnel beneath the Yangtze River for a high-speed railway.

Such progress also means that the China-developed, 148-meter-long shield machine, is coming closer to the zone with the highest level of construction difficulty, said China Railway Tunnel Group Co, builder of what will be a 14.25-kilometer underwater railway tunnel linking Shanghai's Chongming Island with Taicang city, Jiangsu province.