An expert examines the dead whale at a port in Shanghai on March 21, 2017. [Photo/for China Daily]

The dead animal was a fin whale, a second-class national-level protected animal, said Tang Wenqiao, a professor from Shanghai Ocean University, who checked the whale on-site on Tuesday morning.

The whale measured about 22 meters and weighed about 20 tons. Its body was well preserved, except for its missing left pectoral fin, and some parts had already decayed.

Tang said that judging from the whale's wound, the fin was possibly cut by people, and the whale died more than 10 days.

Lu Haibing, owner of a fishing boat, said he first saw the whale on March 19, and the left fin was already missing.

Fishermen reported the sighting of the whale to police at around 1:00 pm on March 20, and were asked to bring the whale back to port.

Police said the authorities have asked marine biology experts to examine the cause of the death.

Although this was the largest whale, this was not the first sighting of a whale near Shanghai. In 2002, a small whale was found stranded at Dishui Lake area. But rescuers managed to help it return to sea. In 1970, a whale was found dead near Luchao Port.

Last week, a sperm whale became stranded and later died in Daya Bay, Guangdong province. An autopsy showed that it was pregnant, and a 110-kilogram male fetus was found dead.

"It is the first time in the world that an unborn baby has been found inside a stranded sperm whale," said Tong Shenhan, head of the Land and Marine Life Research Institute in Xiamen, Fujian province, who participated in the autopsy.