A station of the Xiamen metro Line 2. (Photo/xmgdjt.net)

The first undersea subway tunnel of China started official operation on Dec. 25 as southeast China’s Xiamen announced the opening of its metro Line 2.

The metro line, designed by China Railway Siyuan Survey and Design Group Co., Ltd., is the second metro line of Xiamen. It covers a length of 41.6 kilometers with 32 underground stations.

The undersea section of the metro line is 2,784 meters long, and it takes around 3 minutes to complete the length.

“The undersea section was the hardest part in Xiamen’s history of subway construction,” said Wang Jinlong, chief designer of the metro line, referring to the 2,784-meter tunnel that took the constructers 1,137 days to complete.

“The time explains the difficulty,” Wang added.

The undersea tunnels of Xiamen metro Line 2 and the Hong Kong-Zhuhai-Macao Bridge have accumulated valuable experience and built vital technical reserve for China’s future construction of cross-strait tunnels, said Qian Qihu, academician of the Chinese Academy of Engineering at a recent technical evaluation seminar for the metro line.