Five workers died and one was seriously injured when building in northwest China's Qinghai Province collapsed yesterday afternoon, company sources and the safety administration said.

The accident happened around 4 pm at Jinyuan Cement Factory in Donghe Town of Huzhu Tu Autonomous County.

Workers were putting the finishing touches on the factory's new workshop when it suddenly collapsed, burying six people, said Jin Shenghui, general manager of the Zhengping Group Co., which runs the cement plant.

Three of the victims were already dead when rescuers found them in the debris. Two others died during an emergency rescue, Jin said.

The only victim still alive is being treated at the People's Hospital in the provincial capital of Xining. He is still in critical condition but "might still survive", Jin said, quoting a doctor.

The local work safety supervision administration has launched an investigation into the accident.

The administration gave no comment as to whether the collapse was related to a 6.3-magnitude earthquake that rocked Haixi prefecture yesterday.

Huzhu, in the east of Qinghai Province, is about 40 km northeast of the provincial capital Xining. Da Qaidam, the epicenter of the quake, is 716 km northwest of Xining.

The provincial seismic network monitored more than 550 aftershocks as of Tuesday morning, the largest measured 4.4 on the Richter scale.

The quake and aftershocks cracked walls of some houses near the epicenter but no widespread damage has been reported.

The only injuries, so far, were three mine workers who were slightly hurt while being evacuated.

"Altogether 119 workers underground and 38 above ground were evacuated to safe areas an hour after the quake," said Duan Mingdao, deputy manager of Yihai Energy Company that runs the Dameigou Coal Mine, about 15 kilometers from the epicenter. The three injured workers were sent to the hospital.

Duan said the quake cut the mine's communication network and power supplies for hours but power resumed within the day.

Big cracks were seen on most mining buildings and the workers' dorms were in dangerous conditions. The company bought 20 tents to accommodate its 700-strong workforce.

The mine has suspended operation, Duan said.