China has mobilised more than 50,000 soldiers to help victims of the country's worst earthquake in 30 years, with tens of thousands dead, missing or trapped under crushed houses, schools and factories.

Rescuers are struggling to reach towns and villages devastated by Monday's huge 7.8 magnitude quake in southwestern Sichuan province, which is still being pummelled by wave after wave of terrifying aftershocks.

The death toll was officially nearly 10,000, according to the state-run Xinhua news agency, but that figure was expected to rise dramatically with at least 10,000 people alone buried in Mianzhu city in Sichuan.

Up to 5,000 people have been killed in one district, Beichuan, where 80 per cent of buildings collapsed, according to Xinhua.

"Several thousand" were reported killed or buried in the nearby town of Hanwang after a factory collapsed, while over 600 people died and 2,300 were buried in Shifang city where there was a major chemical leak.

More than 18 hours after the quake struck, there was still little news out of Wenchuan county, a poor mountainous region of around 112,000 people situated in the epicentre.

Hundreds were feared buried at Juyan Middle School in Dujiangyan city, about 50km from the epicentre, and rescuers have pulled about 60 bodies from the rubble so far.

Dujiangyan resident Wen Xiaoping was standing over his mother's body, covered on the ground with a sheet of plastic, after he and his neighbours dug through collapsed rubble to find her.

"I lost everything. I lost my house and I lost my mother," said Wen.

"My brother is in hospital with severe injuries to his chest. I'm waiting for someone to come and pick up the body. But no-one has come yet," he said.

Police were seen pulling out other bodies, many badly battered, from the rubble of one collapsed building, placing them in a row out the front.

Pictures posted on Chinese internet news sites showed rescuers standing atop huge slabs of shattered concrete at the Juyan Middle School as cranes tried to lift away massive chunks of rubble.

Some buried teenagers were struggling to break loose from underneath the ruins, while others were pinned under rubble and crying out for help. Grieving parents watched as cranes were excavating at the site.

Foreigners were among the dead or missing, with 37 tourists killed when their coach was buried in a landslide in Aba prefecture in Sichuan. Officials said they had also lost contact with 15 British tourists, state media reported.

Australian government officials said initial reports indicated that no Australians had been killed or seriously injured in the earthquake.

Prime Minister Wen Jiabao warned the situation in the quake zone was severe as China mobilised a large proportion of its 2.3 million-strong armed forces to spearhead the search and rescue effort.

A total of 16,760 soldiers had already begun relief efforts as of Tuesday morning, while another 34,000 were advancing toward quake-hit regions by plane, train, truck and on foot, Xinhua said.

"The situation is worse than we previously estimated and we need more people here to help," Premier Wen said, speaking at the disaster relief headquarters in Dujiangyan.

President Hu Jintao urged an "all-out" effort to rescue victims and the authorities announced an initial allocation of 200 million yuan ($A30.6 million) of relief funds.

World powers including the United States, the European Union, Russia and Japan rallied around China with sympathy and pledges of help.

The huge quake struck at 2.28pm Monday and rocked skyscrapers up to 1,800km away in cities across China and parts of Southeast Asia, where panicked residents fled into the streets.

The quake hit in the middle of the day when schools, factories and offices were full. While many buildings in larger cities withstood the impact, buildings in rural areas would not have been built to withstand such a large quake.

The area had been rocked by more than 1,180 aftershocks of up to magnitude six as of 5am Tuesday, the Sichuan provincial seismological bureau said.

Relief forces are battling to reach the worst-hit areas of Wenchuan county approaching on foot, Xinhua says, as vehicles are not able to use the road littered with rocks and boulders.

All lines of communication were cut with the county, which is also home to the Wolong Nature Reserve, China's leading research and breeding base for endangered giant pandas. Xinhua later said 60 rare giant pandas at Chengdu Giant Panda Breeding Research Base were safe.

But an official in Wenchuan managed to appeal for emergency aid via a satellite phone, Xinhua reported.

"We are in urgent need of tents, food, medicine and satellite communications equipment through air drop," Xinhua quoted Wang Bin, Communist Party secretary of the county, as saying.

"We also need medical workers to save the injured people here."

The health ministry dispatched emergency medical teams to Wenchuan and the Chinese Red Cross sent tents and quilts.

The quake's epicentre was about 93km from Chengdu, a city of more than 12 million people, and 260km from Chongqing and its 30 million population.

The death toll is the highest for a quake in China since 242,000 people perished when the northern city of Tangshan was flattened in 1976.