Three workers were killed and 15 others injured, after the rooftop of a four-story factory building under construction collapsed in northwest China's Shaanxi Province, said the local production watchdog Friday.

The accident happened at 2:30 p.m. Thursday in Huian Chemical Factory in Yuxia Township in the outskirt of Xi'an, the provincial capital, the source said.

Workers said the collapse might have been caused by the weak supporting foundation of the roof.

The production safety authority is still investigating the accident.

(Xinhua News Agency July 31, 2009)