A 70-year-old man has died after he went missing while swimming at Coogee Beach in Sydney's east.

Emergency services began searching for the man at about 7.45pm on Friday night, after his sister waved down passing police to say she could not find him.

He disappeared when he entered the water at 7pm.

Police searched the sand with torches, while the NSW Ambulance helicopter and a Surf Rescue boat searched the water.

The helicopter spotted the man near the north headland of the beach about 9pm.

He was winched on board and taken to shore, where paramedics performed CPR, but he could not be revived.

In a statement, NSW Police said the man is understood to be an Australian.

"Officers from Eastern Beaches Local Area Command will prepare a report for the Coroner," a spokesman said.