| CHENGDU, China
CHENGDU, China Thousands of Chinese troops are set to join a frantic search for earthquake survivors on Wednesday, with prospects looking increasingly grim for thousands of people buried under rubble and mud.
Some 20,000 troops already searching in the southwest province of Sichuan, where Monday's 7.9-magnitude earthquake crumpled homes, schools and hospitals and cut off some of the worst-hit towns, will be doubled, the official Xinhua news agency reported.
The national death toll from the quake has climbed past 13,000 and is likely to rise steeply after media said 19,000 people were buried in rubble in just one area of Sichuan.
A near overwrought Chinese Premier Wen Jiabao was shown on state television using a bullhorn to urge on rescuers.
"At present the number one thing is still saving people," Wen told local officials, according to Xinhua. "All collapsed buildings must be fully checked. If there is a glimmer of hope, then put everything into rescuing."
But the depth of destruction in the towns and worst-hit mountainous areas suggests that the influx of troops is likely to find many more bodies than survivors among the toppled buildings, which have become grim vigil sites for desperate families.
In Beichuan County, at least 1,000 students and teachers were buried under a seven-storey school building, and rows of apartment blocks in the town collapsed. Locals told Xinhua that up to 8,000 residents may have died.
"People escaped from the buildings but were only devoured by the landslides," one survivor, Lei Xiaoying, told Xinhua. "There was no way to escape."
That scene is repeated in many other places where troops are only now entering after battling rain and severed roads.
State media reported devastation in villages near the epicenter in Wenchuan, a remote county cut off by landslides about 100 km (60 miles) northwest of the Sichuan provincial capital, Chengdu.
About 60,000 people were unaccounted for across Wenchuan.
In Mianzhu, rescuers said the death toll had risen to 3,000. About 500 people were pulled out alive from crushed buildings. An earlier report said 10,000 people there had been buried under rubble.
A further 18,645 people were buried under debris in Mianyang, a city that also covers much farmland, Xinhua said.
The quake was the worst to hit China since the 1976 Tangshan tremor in northeastern China where up to 300,000 died.
Offers of aid have come from all over the world, three months before the Beijing Olympics. The disaster has for now sidelined upbeat propaganda about the games as well as international tensions over recent unrest in Tibet.
Overnight, Chinese President Hu Jintao spoke about the earthquake, as well as Tibet and other subjects, with U.S. President George W. Bush.
Hu told Bush that Chinese people "deeply grieved" the massive loss of life in the earthquake, the Chinese Foreign Ministry said on its Web site (www.fmprc.gov.cn).
Analysts said they did not expect serious economic effects from the disaster, but supply shortages could fuel inflation -- already at a near 12-year high.
(Writing by Chris Buckley; Editing by David Fox)