Residents and troops garrisoned in the town used shovels and their hands to pull survivors and bodies from the rubble much of the day. Several schools collapsed, with the state news agency saying at least 56 students died. Worst hit was the Yushu Vocational School, where Xinhua cited a local education official as saying 22 students died.
Footage on Qinghai Satellite TV showed bodies wrapped in blankets lying on the ground while rescuers pulled shards of concrete from a pancaked school building.
Crews set up emergency generators to restore operations at Yushu's airport, and by late afternoon the first of six flights landed carrying rescue workers and equipment. But the road to town was blocked by a landslide, hampering the rescue as temperatures dropped below freezing. Tens of thousands of the town's 70,000 people were without shelter, state media said.
The airport in Xining, the nearest big city some 530 miles (860 kilometers) away, was filled with Chinese troops in camouflage, firefighters and dozens of rescue workers with sniffer dogs. The airport had been closed to civilian flights for several hours Wednesday night to make way for the rescue effort.
"The situation here is difficult. Most of the buildings have collapsed. A lot of people are seriously injured," said Pu Wu, a director of the Jinba Project, which provides health care training for Tibetan communities. "We are scared. We are all camping outside and waiting for more tents to come."
While China's military is well-practiced in responding to disasters, the remote location posed logistical difficulties. The area sits at around 13,000 feet (4,000 meters) and is poor. Most people live in Jiegu, with the remaining -- mostly herders -- scattered across the broad valleys. The small airport has no refueling supplies, so relief flights were carrying extra jet fuel, reducing their capacity for hauling supplies, state media reported.
The local quake relief headquarters put the death toll at 589 and the injured at 10,000 by early Thursday morning, according to the Xinhua news agency. Wu Yong, commander of the army garrison, said the deaths "may rise further as lots of houses collapsed." Hospitals were overwhelmed, and rescue teams were slowed by damaged roads, strong winds and frequent aftershocks.
Luo Song, a monk from a monastery in Yushu county, said his sister who worked at an orphanage told him three children were sent to a hospital but the facilities lacked equipment.
"She said the hospitals are facing a lot of difficulty right now because there are no doctors, they have only bandages, they can't give injections, they can't put people on intravenous drips," the monk said by phone while on a visit to the southern Chinese city of Shenzhen. China's rural hospitals typically are not well equipped.
Workers released water from a nearby reservoir whose dam was cracked by the quake, according to the China Earthquake Administration.
President Hu Jintao and Premier Wen Jiabao urged "all-out efforts" to rescue survivors and dispatched a vice-premier to supervise the effort. The government immediately allocated $30 million (200 million yuan) for relief, and mobilized more than 5,000 soldiers, medical workers and other rescuers, joining 700 troops already on the ground.
With many people forced outside, the provincial government said it was rushing 5,000 tents and 100,000 coats and blankets to the region, where average daily temperatures were around 43 degrees Fahrenheit (6 degrees Celsius).
The initial quake, measured at magnitude-6.9 by the U.S. Geological Survey and 7.1 by the China Earthquake Networks Center, hit Yushu at 7:49 a.m. (7:49 p.m. EDT, 2349 GMT). It was followed by five more tremors within three hours, all but one registering 5.0 or higher.
Residents of Jiegu, known by Tibetans as Gyegu, about 20 miles (30 kilometers) from the epicenter, fled dazed and sobbing as the ground shook, toppling houses, as well as temples, gas stations, electric poles and the top of a Buddhist pagoda in a park, witnesses and state media said.
"Nearly all the houses made of mud and wood collapsed. There was so much dust in the air, we couldn't see anything," said Ren Yu, general manager of Yushu Hotel in Jiegu. "There was a lot of panic. People were crying on the streets. Some of our staff, who were reunited with their parents, were also in tears."
More than 100 guests of the hotel, which was relatively undamaged, were evacuated to open spaces such as public squares, Ren told The Associated Press by phone. After transporting guests to safety, hotel staff helped in rescue efforts in other buildings, Ren said.
"We pulled out 70 people, but some of them died on the way to the hospital," Ren said, adding other survivors were put in tents in the hotel yard while they awaited assistance.
Many of the students boarded at the schools and were preparing to head to class when the quake struck. One rescue worker said he didn't know how many students had died but he had helped recover several bodies.
"Students just got up and were yet to go to class when the quake happened. I recovered several bodies from the debris and found they were fully dressed," said Zhu Liang, a government worker who joined the rescue operation.
The destruction of schools is an eerie echo of the massive magnitude-7.9 quake that hit neighboring Sichuan province two years ago, leaving nearly 90,000 people dead or missing. Thousands of students among the dead were killed when their schools collapsed. Poor design, shoddy construction and the lax enforcement of building codes were found to be rampant.
Both Wednesday's quake and the one in Sichuan two years ago occurred along the Longmenshan fault, which runs underneath the mountains that divide the Tibetan plateau to the west and the Sichuan plain below.
Messages of sympathy came from the pope at the Vatican, U.N. Secretary-General Ban Ki-moon, as well as the Dalai Lama, the exiled Tibetan leader revered by the often fervently Buddhist Tibetans and reviled by Chinese leaders, who accuse him of fomenting separatism.
Once a trading hub and a gateway to central Tibet, Yushu and surrounding environs were among the Tibetan areas caught up in the anti-government protests that swept the region in March 2008. Tensions have simmered since, and the region has been closed to foreigners off and on.
The garrison of troops who were the first to respond to the quake is stationed in the area to help maintain order. CCTV reported that soon after the quake, troops secured banks, oil depots and caches of explosives.
Associated Press Writers Charles Hutzler and Tini Tran and researchers Zhao Liang and Yu Bing contributed to this report.