A panda that died suddenly last Thursday night was killed by gas poisoning in a zoo in Jinan City of east China's Shandong Province, zoo management said Monday.

Initial investigations showed that the panda died after inhaling gas disinfectant from a nearby former air-raid shelter. The gas was composed of chlorine, chlorine hydride and carbon monoxide, said Liu Jungang, deputy Party secretary of Jinan Zoo.

Workers were disinfecting the air-raid shelter when the gas leaked to the zoo's panda house through an air-pipe.

Police are investigating the case.

The panda was found poisoned at around 7 p.m. and died in a local hospital after three hours of treatment failed.

The female panda Quan Quan, a star at Jinan Zoo and a "heroic mother," had given birth to seven cubs.

Quan Quan arrived at Jinan zoo three years ago. Aged 21, the panda was the equivalent of a woman more than 70 years old.

Giant pandas are among the most endangered species in the world, with only a few thousand living in the wild, mountainous areas of southwest China.