A giant panda that went missing from a nature reserve after China's massive earthquake has returned safely, but two others remain unaccounted for, the state-run news agency says.

The two missing animals, from one of the world's rarest species, were "very likely to be alive" but may be distressed with numerous aftershocks rumbling across quake-stricken Sichuan province, forestry officer Xiong Beirong told Xinhua.

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"Both pandas were adults and they are more capable to escape from dangers than younger ones," Mr Xiong was quoted as saying.

"We hope the two missing pandas are as lucky as their peers."

Workers killed

The magnitude 7.9 quake that devastated large parts of Sichuan on May 12 killed five workers and severely damaged enclosures at the Wolong Giant Panda Reserve, a world-renowned haven for about 60 of the animals.

Two pandas were injured when their houses collapsed, while the others, including 14 cubs born last year, were unhurt, Xinhua says.

Fourteen of 32 panda enclosures were destroyed, with the others badly damaged.

Six pandas escaped, with three quickly found.

The Xinhua report did not say exactly when the fourth panda returned.

Symbol of China

The panda is a national symbol of China, with about 1,590 living in the wild, mostly in Sichuan and the western province of Shaanxi.

Another 180 have been bred in captivity.

The Wolong reserve lies deep in hills outside the provincial capital of Chengdu and is about 30 kilometres from the epicentre of the quake, which caused widespread destruction and killed an estimated 50,000 people.

Emergency supplies of bamboo, apples and veterinary medicine have been rushed to the reserve, officials say.