Man dies after falling from Sydney cliff

A man has died after falling from a cliff into the ocean in southern Sydney, where it's believed he was with friends on the lookout for whales.

A young man has died after slipping and falling from a cliff while whale-watching with a group of friends in southern Sydney.

The man, believed to be aged 18, fell at least 10 metres at Cape Solander in Kurnell about 3.30pm on Monday.

Police, with the help of a rescue helicopter, found him floating in the water and pulled the him - unconscious - to dry land.

Paramedics performed CPR but he could not be revived.

Chief Inspector Chris Hill said early investigations suggested it was a case of misadventure.

"It would appear at this time he was here with a group of friends to go whale watching," he told reporters at the scene.

"They've made their way down to the rock platform ... He's slipped and fallen over the edge and unfortunately died."

The death cames barely six weeks after a man in his 30s fell from the same popular whale-watching spot and died.

Chief Insp Hill urged anyone visiting the area to take heed of warning signs at the lookout.

"Those rocks are very slippery. For your safety, we recommend that you stay up on the whale watching platform and please don't go down on the rocks," he said.

The NSW National Parks and Wildlife Service describes Cape Solander as "one of Sydney's best whale watching spots".

June and July are the best times to see humpback whales as they migrate to warmer waters.