Two men have died despite desperate attempts to revive them after their boat capsized off the coast of Sydney this afternoon.

A third man is lucky to be alive after he managed to swim to shore.

A spokesman for the Westpac Lifesaver Helicopter told ninemsn the three men were in a tinny about 100 metres off the coast of Botany Bay when it capsized after being by a small wave shortly after 1pm.

Two of the men were winched out of the water and received CPR on a helipad for at least half an hour, but could not be revived, the spokesman said.

The three men, who are believed to be family members, were not wearing life jackets at the time, he said.

NSW Police said the third man suffered minor injuries.

Officers at the Miranda Local Area Command and Marine Area Command were called to the scene near Salander Point "following reports of three men in the water", police said.

"It's believed the men were fishing in a small boat when they came into trouble. The boat hit rocks, causing the three men to fall into the water," police said in a statement.

"Emergency services were called and the bodies of two men were winched from the water by a Westpac Helicopter.

"The third man was winched off nearby rocks."

He has been taken to hospital.

Detective Superintendent Mark Hutchings, Commander of the NSW Marine Area Command, said it was a tragic reminder of boat safety during the busy summer period.

"Keeping vigilant and ensuring safety when heading out on the water is often overlooked," he said.

"As the weather has been very unpredictable over the last few months, all boat users must stay alert to weather conditions and are urged to monitor the Bureau of Meteorology.

"Police will continue to be out on the water checking all skippers adhere to the speed limits, respect fellow water users, and don't operate vessels under the influence of drugs or alcohol; just as would be expected out on the roads."

© ninemsn 2014