GUIYANG, June 16 -- Three workers have been rescued but six others remain trapped after the collapse of a steel tunnel at a factory under construction in southwest China's Guizhou Province on Sunday.

The structure of the ferroalloy plant in Yilong New Area of the Bouyei-Miao Autonomous Prefecture of Qianxinan, collapsed at 10:20 p.m. on Sunday. Nine workers were buried in the debris.

The rescued three were injured and rushed to a local hospital, said a government official of the prefecture on Monday.

Rescue work is under way, and the cause of the accident is being investigated.