At least 7,700 people have died in one small town at the epicentre of a huge earthquake that struck southwest China, state media reported on Wednesday.

Only 2,300 people in Yingxiu town survived Monday's quake, local government official He Biao was quoted saying by Xinhua news agency. The town has a population of 10,000.

More than 1,000 of the survivors were seriously injured, the report said.

The quake has left more than 12,000 people dead, according to official figures, although the toll is expected to rise dramatically.

Hampered by shattered roads and driving rain, China has further battled to locate survivors among the tens of thousands of people buried in the rubble of its worst earthquake in 30 years.

The destruction around the epicentre of the 7.9-magnitude quake in the remote county of Wenchuan is massive, with whole mountainsides sheared off, highways ripped apart and building after building flattened.

Rescue teams have been seen pulling bodies and badly injured survivors out of the ruins of schools, factories, hospitals and houses.

China has deployed 54,000 troops in the disaster zone, and the military said it was hopeful it could go ahead with parachute drops and helicopter relief flights which were cancelled on Tuesday because of the thunderstorms.

"As soon as weather conditions permit, airdrops of food and medicine into Yingxiu town will begin immediately," said Lieutenant General Li Shiming of the People's Liberation Army, referring to a badly-hit town in Wenchuan.

However the China Meteorological Authority said more rain was forecast later this week which would raise considerably the risk of new landslides in the mountainous region.

Amid the delays and setbacks, the nation focused on the precious minutes going by for those who were buried under rubble but may have survived.

"Rescuers Race Against Time," the headline of a special front-page report in the China Daily said, above a huge photo of rescuers digging through rubble.

Premier Wen Jiabao, who has been overseeing rescue efforts from the badly-hit city of Dujiangyan, had earlier appeared to express impatience with the pace of relief efforts.

"We must try our best to open up roads to the epicentre and rescue people trapped in the disaster-hit areas," he said.

"At present, we have great difficulties carrying out our rescue work."

A team of 1,300 PLA medics and other troops had managed to reach Wenchuan county around mid-day Tuesday after hiking by foot.

Other small teams were reported to be trickling into the worst-hit area north of the Sichuan provincial capital of Chengdu.

Zhu Jixiang, a Red Cross worker in Mianyang city about 110 kilometres from the epicentre, told AFP by phone that vital supplies were critically short in the worst-hit areas and that medical facilities were overrun.

"No vehicles can access the region. The police and cadres in government agencies are working to clear the roads," he said.

State media has reported that 21.6 million bottles of water will be sent to help survivors of the devastating earthquake.

In towns and villages across a swathe of Sichuan province, heart-rending scenes were played out as grief-stricken families searched for missing loved-ones.

In the city of Mianzhu, where at least 3,000 died, rescuers picked through twisted metal and concrete trying to find people whose voices could be heard coming from the rubble.

"My younger brother is in there," 42-year-old Li -- his eyes bloodshot from sleep deprivation -- said, as his sister-in-law cried next to a heap that was once a Bank of China branch.

The local disaster relief headquarters said rescuers had been able to pull 500 people alive out of the debris of collapsed buildings, but 20,000 in three outer villages were still out of reach.

The full scale of the disaster has yet to emerge as the official media has only been able to give snapshots from different locations.

Xinhua quoted officials from just one city saying 18,645 people were buried there, with thousands were reported buried at single factory complexes.

World powers including the United States, European Union, Japan, the United Nations and the International Olympic Committee rallied with pledges of help.

China welcomed the offers but said on Tuesday conditions were "not yet ripe" to allow in foreign rescue teams, citing damage to transport links.

A Japanese foreign ministry official in charge of emergency aid said Japan had offered China rescue teams with sniffer dogs.

But he added: "We have no dispatch plan at the moment as there has been no request from China."

US President George W. Bush and his Chinese counterpart Hu Jintao discussed the disaster by telephone on Tuesday, and Washington offered half a million dollars in initial disaster aid.

Beijing Olympics organisers said they would scale down the torch relay now going through China -- a further knock to its troubled round-the-world journey after earlier protests over Tibet.

In Beijing, Olympic organising committee spokesman Sun Weide said the relay would be scaled back starting with Wednesday's leg in the eastern province of Jianxi, and would include a minute's silence before runners set off.

The earthquake is the worst in China since 242,000 people perished when the northern city of Tangshan was flattened in 1976.