Four workers were killed and another injured after a tunnel collapsed at a railway construction site in northern China early on Tuesday, local authorities said.

Rocks and earth caved in at about 4 a.m. as workers were digging a new tunnel over a section of the Baotou-Xi'an Railway running through Ordos city in the Inner Mongolia Autonomous Region, according to the region's safety supervision administration.

No further details were immediately available.

Local officials were rushing to the site and investigators were trying to discover the cause and the number of workers on duty at the time.

Construction of the 800.9-kilometer railway began in November. The line will mainly carry coal, linking Baotou in Inner Mongolia and Xi'an, the capital of Shaanxi Province, with stops in Ordos, Yulin and Yan'an.

(Xinhua News Agency March 25, 2008)