Pan Pan, the world's oldest male panda, died age 31 in Sichuan province at 4:35 am on Wednesday.

An autopsy is being carried out to discover the cause of his death, though the circumstances are not thought to be suspicious.

"Pan Pan was equivalent to about 100 human years, but he had been living with cancer and his health had deteriorated in the past three days," said Tan Chengbin, a keeper at the Dujiangyan base of the China Conservation and Research Center for the Giant Panda. "He lost consciousness and did not recover."

Pan Pan was genetically linked to several pandas at the Smithsonian's National Zoo in Washington. A report on the Washingtonian website described Pan Pan as linked to about one-fourth of the world's population of captive-born pandas, including Tian Tian and three cubs raised at the National Zoo in Washington since 2005.

Though born in the wild in Sichuan's Baoxing county in 1985, Pan Pan lived in captivity from just a few months old.

"Panda Grandpa", as he became known, was diagnosed with cancer in June, and also suffered from common old-age conditions, such as cataracts and poor dental health.

A reporter from Xinhua News Agency, who last saw Pan Pan on Dec 21, said he was in a "nursing home" for elderly pandas, and though he was very thin, he was in good spirits.

"When the keeper called his name and offered him food, usually steamed cornbread or fresh bamboo leaves, he was able to respond and move outside to eat," the reporter said.

Pandas are notoriously difficult to breed, but Pan Pan lived a particularly active life for a panda and fathered many cubs over the past 20 years, and is said to have had more than 130 descendants.

The average life span of wild pandas is normally 20 years, but those in captivity usually live longer.