Twenty-three people were killed and five seriously injured when a vehicle carrying railway construction workers overturned in northwest China's Gansu Province on Saturday, the official Xinhua news agency said.
China has invested heavily on railway infrastructure to connect the vast country during years of strong economic growth.
But authorities recently suspended new rail projects after a collision between two high-speed trains in July killed 40 people and fanned public anger over transport safety issues.
Shanghai authorities also came under fire in September after the worst subway accident in 42 years raised fresh concerns that the world's second-largest economy was sacrificing safety in the rush to develop.
Xinhua said the vehicle overturned in a mountain tunnel that was still under construction as part of a railway track in Manwa township in Lintao County.
It was not immediately known how many people were in the vehicle, or whether all of those killed or injured were construction workers.
An initial investigation showed brake failure was the likely cause of the accident, a spokesman with the local railway authorities was quoted as saying by Xinhua.
(Reporting by Jacqueline Wong; Editing by Paul Tait)