A shallow 6.6-magnitude earthquake struck China's southwestern Sichuan province, with the US Geological Survey saying "significant casualties" were likely, five years after a massive quake devastated the same region.

No casualties or damage have yet been reported after the quake, which hit just after 8:00 am (0000 GMT) at a depth of 12 kilometres (7.4 miles).

But the USGS said on its website that "significant casualties are likely".

"Extensive damage is probable and disaster is likely widespread," it said.

"Past events with this alert level have required a national or international level response."

The Xinhua state news agency said it was felt in the provincial capital of Chengdu 114 kilometres to the east.

In 2008 the province saw one of the country's worst earthquakes in decades, with 87,000 people missing or dead.

That quake, which struck west-northwest of Chengdu, generated an outpouring of support, with volunteers rushing to the scene to offer aid and then-premier Wen Jiabao also visiting.

The disaster flattened swathes of the province along with parts of neighbouring Shaanxi and Gansu.

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

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

Earthquakes frequently strike the country's southwest, with twin tremors in neighbouring Yunnan province last September triggering landslides that left at least 80 people dead.

Houses were toppled and people slept outdoors for fear of aftershocks, as emergency workers struggled to clear mountain roads blocked by the landslides to reach survivors.

A magnitude-5.5 earthquake in Yunnan last June killed four people and injured more than 100. Another 5.4 tremor the year before near the border with Myanmar left 25 people dead and injured 250.