Local officials said 85 percent of the buildings had been destroyed.
Residents and troops garrisoned in the town used shovels and their hands to pull survivors and bodies from the rubble much of the day Wednesday. Several schools collapsed, with the state news agency saying at least 56 students died. Worst hit was the Yushu Vocational School, where the officials Xinhua News Agency cited a local education official as saying 22 students, 20 of them girls, died.
State broadcaster CCTV showed footage of rescuers working at night, picking through the rubble aided by torchlights fixed to their safety helmets. A group of workers found a girl trapped for more than 12 hours under a heap of debris.
"I can't feel my arm," said the girl, who was curled up with her back to the workers. The workers talked to her and fed her water as others searched for pieces of wood to prop up the rubble that had entrapped her. As rescuers gingerly pulled her out and carried her to a stretcher, she could be heard saying: "I'm sorry for the trouble. Thank you, I will never forget this."
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.
The death toll had risen to 589 by early Thursday, with more than 8,000 others injured, the Ministry of Civil Affairs said in a statement. About 15,000 houses had collapsed and 100,000 people need to be relocated, it said.
Many survivors spent the night in the cold outdoors, wrapping themselves in thick cotton blankets and lying on thin pads on the ground with cardboard boxes serving as makeshift pillows. Others spent the night in quake-damaged cars, covering exposed areas with sheets of plastic, CCTV footage showed.
Xinhua said temperatures in the area can fall below freezing at night.
The airport in Xining, the nearest big city 530 miles (860 kilometers) away, was filled in the predawn hours Thursday with Chinese troops in camouflage, firefighters and rescue teams leading dozens of sniffer dogs. They were whisked onto waiting buses for the difficult drive to the quake zone, which takes 12 hours under the best of conditions.
Yang Xuesong, a rescuer from Shandong province in eastern China, said his biggest concern was the altitude. "This is the highlands. I don't know if the search dogs can get used to it," he said.
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 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."
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.
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.
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 a series of tremors.
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.
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 U.S. Secretary of State Hillary Rodham Clinton and the White House, 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.
Houston Rockets star Yao Ming has set up a hotline to help North American Chinese residents reach family and friends in China. The hotline number is (718) 766-9636. A recorded message in English and Mandarin asks the caller to enter the phone number of the person they are trying to reach in China.
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.
Associated Press Writers Charles Hutzler, Tini Tran and Gillian Wong and researchers Zhao Liang and Yu Bing contributed to this report from Beijing.