Construction work on a tunnel to carry China's first subway line under the Yellow River was completed on Monday in Lanzhou, capital of Northwest China's Gansu province.

The 317-meter long section of Lanzhou Subway Line 1 runs 40 meters beneath the riverbed.

It is part of a 2,119-meter long stretch of tunnel, completion of which paves the way for a parallel tunnel to be built.

Work on both tunnels is scheduled to be complete by the end of the year.

Wu Dun, project manager, said the team faced technological difficulties and risks during construction.

Qian Qihu, a tunnel expert and fellow researcher at the Chinese Academy of Engineering, has previously described building a subway line under the Yellow River as a "world-class" engineering problem.