Thousands of rescue workers combed through flattened villages in southwest China on Sunday in a race to find survivors from a powerful quake as the toll of dead and missing rose past 200.

Dressed in bright orange uniforms, rescuers battled their way up mountain paths strewn with wreckage to reach isolated parts of Sichuan province on the edge of the Tibetan Plateau.

Army troops dressed in camouflage worked through the night, searching villages where houses had been destroyed for survivors and treating those injured in the quake.

China's new Premier Li Keqiang has rushed to the disaster zone and was shown by state broadcaster CCTV eating breakfast in a tent. He told state media that "the rescue effort is our first duty".

Li said on Saturday that the first 24 hours was "the golden time for saving lives", as China's new leaders respond to a fresh disaster five years after another Sichuan earthquake left more than 90,000 people dead or missing.

But the rescue operation was hampered by huge queues of traffic -- some stretching back for 20 kilometres (12 miles) -- clogging roads into the disaster zone.

"We really want to go in and help people, but instead we are waiting in traffic," one frustrated relief official said in his car, as large numbers of volunteer rescuers from local communities tried to head to the zone.

Boulders the size of cars littered streets in Lushan county, the epicentre of the earthquake.

"Three people died in that building, and no one wants to live in this area any more because it is too dangerous," a 45-year man surnamed Yang told AFP, surrounded by rubble from the quake.

More than 1,100 aftershocks have followed since the quake struck Sichuan province on Saturday morning. Chinese seismologists registered the tremor at 7.0 magnitude while the US Geological Survey gave it as 6.6.

At least 179 people have been confirmed dead, 24 are missing and nearly 11,500 were injured, the Ministry of Civil Affairs said.

Firefighters helped by sniffer dogs have pulled 91 people alive from the rubble, the Xinhua news agency said, citing the Ministry of Public Security.

At Lushan People's Hospital, a steady stream of ambulances continued to arrive in the early hours of Sunday. Most victims were taken to tents erected in the grounds of the hospital, where doctors treated the wounded.

A 68-year-old woman with a broken arm spoke of the terror she experienced when the earthquake struck.

"It was as if the mountain was alive," she told AFP. "Now I have no home to go. So I don't know what I am going to do."

Quake-prone Japan, which has been mired in tension with China over a high-seas territorial dispute, offered any help that is required.

"Japan is ready to offer its maximum support," Prime Minister Shinzo Abe said in a message to Chinese President Xi Jinping and Premier Li, according to Japan's foreign ministry.

China responded that overseas assistance was not needed at the moment but that it would contact Japan if that changes, the ministry said.

More than 17,000 Chinese soldiers and police have joined the rescue mission and five drones were sent to capture aerial images, Xinhua said, as well as aircraft carrying out rescue and relief work.

A military vehicle carrying 17 troops headed for the quake area plummeted over a cliff on Saturday, killing one soldier and injuring seven others.

The disaster has evoked comparisons to the 2008 Sichuan quake, the country's worst in decades, and President Xi ordered all-out efforts to minimise casualties, Xinhua said.

The 2008 quake generated an outpouring of support, with volunteers rushing to the scene to offer aid and then-premier Wen Jiabao also visiting.

But public anger erupted after the discovery that many schools fell while other buildings did not, creating suspicions of corruption and corner-cutting in construction.

The deaths of the children became a taboo subject in the heavily controlled domestic media and social media websites.

But the response on China's Twitter-like "weibo" sites to Saturday's quake has overwhelmingly been one of support for rescue efforts, with thousands pledging to donate money and others mourning the victims.

Earthquakes frequently strike China's southwest. In April 2010, a 6.9 magnitude quake killed about 2,700 people and injured 12,000 in a remote area of Qinghai province bordering the northwest of Sichuan.

Some facts about China's quake zone
Beijing (AFP) April 20, 2013 - The area of southwestern China struck by a violent tremor on Saturday has witnessed some of the world's deadliest earthquakes.

The area sits on the boundary between two of the Earth's tectonic plates, the Indian and Asian plates, which are constantly grinding against each other.

The region is unusual geologically because of the steep slopes at the boundary between the Sichuan Basin and the Tibetan plateau, according to seismologists.

The elevation rises by about 3,500 metres (11,500 feet) over only about 50 kilometres (about 30 miles).

Earthquakes are frequent along the fringes of the Tibetan plateau, which was raised when India collided into Eurasia starting some 50 million years ago.

It is this powerful thrust that created the Himalayas and its highest peak, Mount Everest, which reaches 8,848 metres (29,029 feet). The mountains continue to reach skyward to this day, propelled by unstable tectonic terrain.

The deadliest earthquake to rock the Tibetan plateau in the 20th century was in 1920 when 230,000 people died in Gansu province. Another quake measuring 8.0-magnitude struck Sichuan in May 2008 leaving nearly 87,000 dead or missing.

Jiang Haikun, an official with the China Earthquake Networks Centre's forecasting department, said Saturday's quake was formed in the same way as the 2008 quake.

Both quakes occurred on the Longmen mountain fault zone, he said, which tended to produce powerful tremors along a 500-kilometre-long belt.

China earthquake timeline
Beijing (AFP) April 20, 2013 - A strong 6.6-magnitude earthquake struck China's southwestern Sichuan province Saturday, killing at least 56 people and injuring hundreds. Here is a list of other deadly quakes in the country:

-- September 7, 2012: Two earthquakes strike the southwestern province of Yunnan, killing at least 81 people.

-- June 24, 2012: An earthquake with a magnitude of 5.5 hits a mountainous area on the border of Sichuan and Yunnan provinces, killing at least four people and injuring more than 100.

-- March 10, 2011: A quake with a 5.4 magnitude strikes a remote area of southwest China bordering with Myanmar, killing 25 and injuring 250.

-- April 14, 2010: A quake with a magnitude of 6.9 kills about 2,700 people and injures another 12,000 in the northwestern province of Qinghai.

-- August 30, 2008. Forty people die after a 6.2-magnitude earthquake strikes Panzhihua city, Sichuan province.

-- May 12, 2008: A 8.0-magnitude quake strikes Sichuan, leaving nearly 87,000 dead or missing. Another 4.45 million are injured in the worst quake disaster to hit China in more than three decades.

-- July 23, 2006: 22 people are killed and 106 injured as an earthquake measuring 5.1 hits Yunnan. More than 6,000 homes are destroyed and 38,000 buildings damaged across 13 municipalities.

-- February 24, 2003: A violent earthquake measuring 6.8 takes 268 lives in the far-western region of Xinjiang and causes significant damage.

-- January 10, 1998: Forty-seven people are killed and 9,000 injured in a quake measuring 6.2 that in the northern province of Hebei.

-- February 3, 1996: A quake measuring 7.0 near the city of Lijiang in Yunnan kills 228 people and seriously injures 3,700.

-- October 24, 1995: An earthquake measuring 6.5 kills 52 in Yunnan.

-- April 26, 1990: A 6.9-magnitude earthquake in Qinghai kills 126.

-- August 23, 1985: An earthquake measuring 7.4 in Xinjiang kills 67.

-- July 28, 1976: The industrial city of Tangshan, 200 kilometres (125 miles) east of Beijing, is levelled by an earthquake measuring 7.8 on the Richter scale (8.2 according to sources outside China). Beijing puts the official death toll at 242,000, with 164,000 seriously injured, although Western sources say the toll could be much higher.

-- February 4, 1975: A quake measuring 7.3 in the northeastern province of Liaoning claims 1,300 lives.

-- May 11, 1974: Ten thousand die in Sichuan and Yunnan after an earthquake of 7.1 magnitude.

-- January 5, 1970: An earthquake measuring 7.8 in Yunnan leaves 15,621 dead.

-- December 26, 1932: An 7.6-magnitude earthquake kills 70,000 people in the northwestern province of Gansu.

-- May 23, 1927: Forty-one thousand people die in Gansu in an earthquake measuring 8.0.

-- December 16, 1920: An earthquake measuring 8.5 in Gansu kills 230,000 people.