KUNMING, May 9 (Xinhua) -- The construction of a tunnel along a section of the China-Myanmar international railway is underway in southwest China's Yunnan Province, according to the local railway authorities.

The Dalin (Dali-Lincang) railway project department of the Railway No. 10 Engineering Group Co., Ltd said that, so far, more than 3,700 meters of the tunnel has been excavated.

The Dali-Lincang Railway, with a length of 202 km and a designed speed of 160 km per hour, is a key section of the China-Myanmar international railway. It is scheduled to be completed and open to traffic in 2021.

Construction on the 10.6 km Hongdoushan Tunnel started in May 2016. However, toxic gases were detected in the tunnel in May 2017.

The project's construction contractor said it has worked with universities and institutes to solve the problem, and the construction has proceeded steadily.