One worker was killed and three others injured after a mechanical malfunction inside a tunnel on the Qinghai-Tibet railway, the website caixin.com reported on Tuesday.

A problem with a cargo train's supercharger occurred at 11 pm on May 13 at the Keke-Xining section of the Qinghai-Tibet railway in Qinghai province, causing the train to halt, according to the Qinghai-Tibet Railway Company.

The machine was repaired, and the train continued on its route.

But on May 14, the problem happened again inside the Guanjiao tunnel.

The malfunction caused the train to stop and release a heavy black smoke, causing all four of the train's workers to choke and lose consciousness.

A rescue team was sent by the company after one of the workers woke up and called for help.

The train driver, Liu Jiankuang, died despite medical efforts, and the other three were in stable conditions.