Beijing  - Troops walked Tuesday to towns and villages near the epicentre of a devastating earthquake that killed about 12,000 people and cut off tens of thousands in south-western China, while at least 10,000 people were buried in one city.

The Civil Affairs Ministry said the death toll had risen to 11,921 since a quake measuring 7.8 on the Richter scale caused widespread damage Monday to south-western China.

About 60,000 people in Sichuan province's Wenchuan county had been out of contact with authorities since Monday while the State Seismological Bureau reported a
6.1-magnitude aftershock in Wenchuan Tuesday afternoon.

All roads to Wenchuan were blocked, but Premier Wen Jiabao, who was overseeing relief work 100 kilometres away in Dujiangyan county, ordered an all-out effort to open a route to Wenchuan as soon as possible, the official Xinhua news agency said.

Some troops walked to Wenchuan from Dujiangyan and other nearby counties despite heavy rain and aftershocks, the agency said.

About 1,300 rescue and relief troops arrived mid-afternoon in Wenchuan's Yinxiu township, 20 kilometres from Dujiangyan, as part of about 50,000 troops and police sent to Sichuan and other affected areas.

Military doctors and soldiers began searching for survivors and treating injured people in Yingxiu, but it was unclear when the first rescuers would reach Wenchuan county town.

An officer leading the advance troops told state television that the damage in Yingxui was "especially severe," with most roads and bridges damaged.

The military planned to send planes to bring back aerial photographs of the disaster area, but it was still impossible to land planes or helicopters in Wenchuan.

State media said the heavy rain Tuesday had also forced the army to cancel a plan to drop paratroopers into Wenchuan.

"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 Xinhua earlier by satellite telephone.

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

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, Wang 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.

The local government of Mianzhu reported that thousands of people were buried and 2,000 had been confirmed dead, Xinhua said.

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

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

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

The central government allocated 860 million yuan (123 million dollars) for relief operations while the Chinese Red Cross collected 65 million yuan (9 million dollars), and donations were promised by many foreign governments.

The earthquake struck at 2:28 pm (0628 GMT) Monday in Wenchuan county, 95 kilometres west-north-west of Chengdu, 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)