NANJING - Four sperm whales were dead by Saturday one day after being stranded on the beach in east China's Jiangsu province, local authorities said.

The whales were found alive at 6 am Friday on the beach of Xintan Salt Field in the city of Yancheng, and died despite human rescue efforts, said a spokesman with the city government.

By Saturday morning, the four were confirmed to have no vital signs, said Xu Xinrong, a senior animal researcher with the Nanjing Normal University.

It was the second time of mass beaching of whales in China, following that in 1985, when six whales died of beaching in southeast China's Fujian province, said Xu.

He said mass beaching of whales was a natural phenomenon and it was hard to find the exact cause for their beaching.

Among the four, the heaviest weighed 30 to 40 tonnes, and the lightest weighted nearly 20 tonnes.

Local fishery and border control departments are guarding the whale bodies until final disposal decisions came from authorities.

Based on previous international routines, their bodies would be buried, used for specimens or dragged back to the sea, said Xu.