Early on Thursday, the official estimated death toll from the Monday quake stood at nearly 14,463, unchanged from the previous day. In all, about 10 million people have been directly affected by the quake, according to the Xinhua news agency.

But as rescuers pick through towns turned to rubble in Wenchuan and other counties nearest the earthquake's epicentre, the toll of missing -- and probably dead -- is likely to balloon.

"In one minute the city we know flew away. I never dreamt it could happen," said He Lixia, a kindergarten teacher in Dujiangyan, where many residents slept outdoors, fearful of more quakes and building collapses.

"My father and mother are dead. My son was crushed under his school. My wife's office has collapsed and her phone is not working," said a man wandering outside one encampment there.

In Shifang, another small Sichuan city that also covers many villages, 30,000 of some 430,000 residents were missing or out of contact, local officials told Xinhua.

The ruling Chinese Communist Party's Standing Committee met late on Wednesday to assess the calamity that has thrown a dark shadow over preparations for the Beijing Olympics in August.

The meeting ordered fresh waves of soldiers and paratroopers to help, and the government announced 90 more helicopters -- in addition to 20 already deployed -- will try to reach areas where buckled roads have frustrated rescuers, state media reported.

"As long as there is a glimmer of hope, spare no efforts in rescuing," the Party leadership ordered, according to Xinhua. "Ensure social stability in the disaster zone."

But now, into the fourth day since the 7.9 magnitude quake, hopes of pulling many survivors from crumpled schools, homes and factories appear increasingly dim.

A paramilitary officer who arrived at Wenchuan, at the epicentre, told Sichuan TV that a third of houses there had been destroyed and more than 90 percent damaged.

Officials have also warned of dangers from increased strain on local dams as well as mudslides on brittle hillsides where rain has been forecast over the next few days.

Landslides had blocked the flow of two rivers in northern Qingchuan county, forming a huge lake in a region where 1,000 have already died and 700 are buried, Xinhua said.

"The rising water could cause the mountains to collapse. We desperately need geological experts to carry out tests and fix a rescue plan," Xinhua quoted Li Hao, the county's Communist Party chief, as saying.

Premier Wen Jiabao, a geologist himself, has criss-crossed the disaster zone and made emotional appeals to workers and comfort orphaned children.

"To be responsible to the people, be responsible to history, we must do rescue organisation work at this crucial moment," he said late on Wednesday, according to Xinhua.

The quake was the worst to hit China since 1976 when up to 300,000 died. Leading disaster modelling firm AIR Worldwide said the cost of the quake was likely to exceed $20 billion.