A severely decomposed whale carcass believed to have died for some time has been found on the shores of Sai Kung.

The Agriculture, Fisheries and Conservation Department on Thursday said it had received a report in the morning about the discovery of a suspected whale carcass in Ham Tin Wan.

It said a preliminary assessment found that the carcass measured about 11 metres in length, but noted that it would be impossible to conduct a necropsy to determine the animal's cause of death because of its "severe decomposition".

Authorities added staff members were working to dispose of the carcass and clean up the area, which was expected to be completed on Friday.

"The deceased whale was not a local species. It is preliminarily believed to be a baleen whale," the department said.

"Based on the degree of decomposition of the carcass, it is estimated to have been dead for some time. It is believed that the carcass drifted into the waters of Ham Tin Wan from the open seas."

Baleen whales typically forage in the cold, high-latitude waters around the Arctic and Antarctic during the summer, while migrating to warmer, low-latitude or tropical waters for breeding and nurturing their young in the winter.