The tremor triggered a power outage but telecommunication service remained normal in Yingjiang, which has a population of 300,000 people and is home to many ethnic groups.

Altogether seven aftershocks, measuring up to 4.7 degrees on the Richter scale, has jolted the quake-prone county since the first tremor.

Experts have not ruled out the possibility that stronger quakes might hit the region later and they could not say for sure that the first magnitude-5.8 tremor was the main quake, according to Gu Yishan, an expert with the Yunnan provincial earthquake bureau.

The magnitude-5.8 tremor was the largest of more than 1,200 minor tremors over the last two months in the region, said Liu Jie, a director with the earthquake forecast department in the China Earthquake Networks Center.

According to Gu Yishan, the frequent tremors in the past months have already done some damages to buildings in the county, which might have worsened Thursday's disaster.

Shallow focus, along with the fact that the epicenter was very close to densely-populated county seat, were also factors behind the damage, he added.

Between 1991 and 2008, eight earthquakes registering higher than 5 magnitude on the Richter scale hit the county, about 700 kilometers west of provincial capital Kunming, said Chen Jianmin, director of the China Earthquake Administration.

A Magnitude-5.9 earthquake struck the county in August 2008, leaving three people dead and 106 injured, said CENC researcher Sun Shihong.

Nearly 1,000 soldiers have been sent to join the rescue operation.

Chinese Vice President Xi Jinping called for all-out measures to save lives and demanded adequate food, clean water and clothes for the affected people.

Provincial governor Qin Guangrong called upon relevant authorities to save injured people and evacuate disaster-hit residents.

The provincial disaster-relief and civil affairs authorities have launched an emergency response plan.

The National Committee of Disaster Reduction, Ministry of Civil Affairs and Yunnan's provincial government have dispatched 9,700 tents, 13,000 quilts, 13,000 clothes and other materials to the quake-hit region.

Central ministries and provincial government departments have sent working groups to Yingjiang to provide expertise and assistance.

The Ministry of Land Resources said in a statement on its website that it initiated a grade IV emergency response following the quake and sent a team of experts to the quake zone to help with relief work.