Nearly 26,000 people remained buried in collapsed buildings from Monday's magnitude-7.9 earthquake, and the death toll of almost 15,000 was expected to climb as relief operations spread into the mountains of Sichuan province. The quake triggered landslides that blocked roads to the hardest-hit areas.

Lines of buses and cars, many with red banners carrying political slogans, filled highways leading north from the provincial capital of Chengdu, near the epicenter of Monday's quake. They were joined by trucks carrying cranes, front-end loaders and tarpaulins.

Even as the rescue effort seemed to gather momentum, speeded by clearing weather after two days of rain, caring for tens of thousands of people made homeless across the disaster zone has stretched thin the government's resources.

Homeless victims begged for aid on roadsides, and people settled in for a third night in a growing sprawl of refugee camps littered with garbage. In Hanwang, a town in one of the hardest-hit counties, survivors stood hoping for handouts from cars, jostling to reach to one vehicle from which a passenger passed bottled water out the window.

"I'm numb," said Zhao Xiaoli, 25, a nurse working at a triage center in a tire-factory driveway. "The first day, hundreds of kids died when a school collapsed. The rest who came in had serious injuries. There was so little we could do for them."

Damage to the two-year-old Zipingpu Dam threatened downstream communities still digging out from the quake. At least 2,000 soldiers were sent to the dam, the official Xinhua news agency said. Four-inch cracks scarred the top of the dam, and landslides had poured down the surrounding hills, the business magazine Caijing said on its Web site in a report from the scene.

Although the government pronounced the dam safe late Tuesday after an inspection, Caijing said its waters were being emptied to relieve pressure. The Ministry of Water Resources issued a notice to check reservoirs nationwide, while the economic planning agency said nearly 400 dams, most of them small, were damaged by the quake.

Hundreds of rivers snake through the mountainous Tibetan plateau before descending into the fertile Sichuan basin, where they provide critical irrigation.

The Three Gorges Dam, the world's largest, is about 350 miles east of the epicenter. The information office of State Council Three Gorges Construction Committee said earlier this week that there was no damage to the dam.

The official death toll rose yesterday to 14,866, and in Sichuan province, 25,788 people were buried, the provincial vice governor, Li Chengyun, said, according to Xinhua.

An already-massive military operation gathered pace with close to 100,000 soldiers and police mobilized. After two days of rain that prevented relief flights, People's Liberation Army helicopters flew 90 sorties to the epicenter in Wenchuan County and other areas to drop food, medicine and tents and ferry out 156 injured people, Xinhua reported.

Despite the devastation, China has rejected offers of help from foreign aid workers, including search-and-rescue experts from Australia, dog handlers from the Czech Republic, and firefighters from Japan.

"Transportation in affected areas is obstructed, and it is impossible for our rescue teams to reach the disaster-hit areas. So the conditions are not yet ripe for us to allow international rescue teams into China," Wang Zhenyao, head of the Civil Affairs Ministry's relief department, told reporters.