At least 23 railway workers were killed and five others were seriously injured when a truck transporting them to work overturned in northwest China.

The accident happened early Saturday in Gansu province when the truck with a driver and 27 passengers aboard overturned in a mountain tunnel.

The official news agency Xinhua says the workers were being taken to a railway construction site. Twenty-one people were killed instantly and two more died in a hospital. The others remain in serious condition.

Xinhua says a preliminary investigation determined that brake failure was the cause of the accident.