Beijing - Tens of thousands of people remained cut off early Tuesday in south-western China, as troops continued efforts to reach towns and villages near the epicentre of a devastating earthquake that killed more than 9,000 people.

About 60,000 people in Wenchuan county, Sichuan province, had been out of contact with authorities since an earthquake measuring 7.8 on the Richter scale caused widespread damage to south-western China on Monday, the official Xinhua news agency said.

All roads to Wenchuan remained blocked, but Premier Wen Jiabao, who travelled to Sichuan to oversee relief work, had ordered all-out efforts to open a route to the county by midday Tuesday, the agency said.

Military planes also planned to fly to Wenchuan, and the Army was considering dropping paratroopers into the area if it was still impossible to land planes there.

"There is still no news about the situation in the townships of Yingxiu, Wolong and Xuankou, which are located exactly at the epicentre," Wang Bin, county secretary of China's ruling Communist Party, told the agency by satellite telephone.

Wang said that the three townships have a total population of more than 24,000.

Wang said the county, which has a population of about 105,000, had confirmed at least 57 dead and more than 300 seriously injured after the earthquake.

It was only a "rough number of casualties at the county seat," he told the agency.

"The figure is highly possible to rise as the casualties in the mountainous area is not available," he said.

Wang said that more than 30,000 people were camped outside in the county town despite heavy rain.

"We are in urgent need of tents, food, medicine and satellite communications equipment through air drop," he said. "We also need medical workers to save the injured people here."

Hundreds more people are feared dead in other areas of Sichuan after they were buried in collapsed schools and factories by Monday's earthquake.

Nearby Beichuan county earlier reported that between 3,000 and 5,000 people were feared dead, after the earthquake caused 80 per cent of buildings to collapse.

About 1,000 children and teachers were believed to be trapped under rubble after school buildings collapsed onto them in Beichuan.

Hundreds of others were still buried under debris from two chemical factories in Sichuan's Shifang city, state television said.

The earthquake struck at 2:28 pm (0628 GMT) Monday in Wenchuan county and could be felt in cities hundreds of kilometres away, including Beijing, Shanghai, Hong Kong and Bangkok.

It was the deadliest earthquake in China since 1976, when an estimated 242,000 people died in the northern city of Tangshan, near Beijing. (dpa)