The China Earthquake Networks Centre put the biggest shock at magnitude 7.1, although the US Geological Survey put it at 6.9. The Haiti quake which killed more than 200,000 and left 1m homeless in January was magnitude 7. The China Earthquake Administration said phone lines were down, hindering rescue efforts, while workers were racing to release water from a cracked reservoir.
At least 400 people have been killed and more have been injured or trapped in rubble after a series of earthquakes in north-west China.
Officials said more than 10,000 people were injured and six quakes hit Yushu county, Qinghai province.
Army trucks have been sent to the remote area, 480 miles away from the provincial capital, Xining, to aid rescue and relief efforts. Witnesses reported the collapse of many brick and wood buildings, with people scrabbling through the debris to free those trapped inside.
Half the buildings at the Yushu vocational school are said to have collapsed.
Xie Caishu, Qinghai armed police corps captain, told state media more than 600 rescuers from the paramilitary police had arrived in the country, but that there was a shortage of disaster relief gear and equipment.
"The need of relief equipment far exceeds supply, including tents, temporary housing, mobile kitchens, power generators. We have reported it to higher levels, who guarantee that relief supplies will be airlifted to Yushu in hours," Xie said. Power and water supplies have been cut although some early reports suggested larger buildings had stood firm. The population is relatively scattered, making it hard to assess damage.
The China Earthquake Networks Centre put the biggest shock at magnitude 7.1, although the US Geological Survey put it at 6.9. The Haiti quake which killed more than 200,000 and left 1m homeless in January was magnitude 7. The China Earthquake Administration said phone lines were down, hindering rescue efforts, while workers were racing to release water from a cracked reservoir.
In Jiegu, a township near the epicentre, more than 85% of houses collapsed, while large cracks appeared on buildings still standing, the official Xinhua News Agency cited Zhuohuaxia, a local publicity official, as saying.
"The streets in Jiegu are thronged with panic and full of injured people, with many of them bleeding from their injuries," he said. One local official was quoted by the BBC saying: "We have nothing now. The loss is huge."
Map: China earthquake, Qinghai province Map: China earthquake, Qinghai province
The provincial government and Red Cross are sending supplies of tents, warm clothing and blankets amid fears that thousands have been left without shelter in near-freezing temperatures.
The main quake sent residents fleeing as it toppled houses made of mud and wood, said Karsum Nyima, the Yushu county television station's deputy head of news, speaking by phone with broadcaster CCTV.
"In a flash the houses went down. It was a terrible earthquake," he said. "In a small park there is a Buddhist tower and the top of the tower fell off.
"Everybody is out on the streets standing in front of their houses, trying to find their family members," he said, adding that school buildings had not collapsed but students had been evacuated and were assembled in outdoor playgrounds.
Yushu county is a largely Tibetan area of Qinghai. The province and other parts of China's north west have suffered repeated tremors in recent years.
A local government website puts the county's population in 2005 at 89,300 people, mostly herders and farmers. State television showed footage of paramilitary police using shovels to dig around a house with a collapsed wooden roof. A local military official, Shi Huajie, told state broadcaster CCTV that rescuers were working with limited equipment.
"The difficulty we face is that we don't have any excavators. Many of the people have been buried and our soldiers are trying to pull them out with human labour," Shi said. "It is very difficult to save people with our bare hands."
Wu Yong, a local military chief, said medical workers were needed but roads leading to the airport had been badly damaged by the quake, creating difficulties for people and supplies to be flown in.
The epicentre of the first quake was located 235 miles south-south-east of Golmud, a large city in Qinghai, at a depth of six miles, the US Geological Survey said.
Ten minutes later the area was hit by a magnitude 5.3 quake, which was followed after two minutes by another measuring 5.2. Both the subsequent earthquakes were measured at a depth of six miles. Another quake measuring 5.8 was recorded at 9.25am.
Two years ago a massive quake in nearby Sichuan left an estimated 90,000 dead or missing.
Dr David Rothery, of the Open University's department of earth & environmental sciences, said: "Like the Haiti quake, it happened when the ground either side of a fault slipped sideways. In this case it was a consequence of India's northward collision into Asia, which for millions of years has slowly been forcing the Tibetan plateau out towards the east."
But the Qinghai quake was at a slightly more shallow depth than that which struck Haiti, said Rothery. "When quakes are shallow, the shaking of the ground is more. Earthquakes are common in this region, but there has not been anything so big within 200 km of the current epicentre since at least 1900.
"As usual in earthquakes, people have died because of the collapse of cheaply constructed buildings, in a poor region where it seems little regard has been paid to building codes that could have offered better protection to the people inside."
