A colossal tunnel boring machine named Dinghai began excavating from the land section into the sea section at 42 meters below sea level near Zhoushan City in east China on Tuesday, marking the beginning of an "undersea journey" for the construction of world's longest undersea high-speed railway tunnel.

With a maximum depth of 78 meters, the Jintang Undersea Tunnel will have a total length of 16.18 kilometers, spanning from Ningbo City's Beilun District to Jintang Town in Zhoushan City in east China. It is an important part of the Ningbo-Zhoushan Railway.