The first driverless subway line is under construction in the city of Chengdu, capital of southwest China's Sichuan Province. The tunnel was dug through on Tuesday, according to the subway constructors.

The No. 9 Line of Chengdu subway is a project co-built by Chengdu Rail Transit Group Co., Ltd. and China Railway Group Ltd.

Construction of the subway line started at the end of 2016 and it's set to become the first fully-automatic driverless subway line in southwest China.

Phase-I project runs approximately 22 km, with a designed top speed of 140 km per hour, with 13 stations planned.

The subway line is scheduled to be operational by the end of 2020.