A search is underway for a 78-year-old man who was thrown into the sea after his boat capsized south of Sydney.

Emergency services were called to Seawall Road, Port Kembla in the Illawarra following reports of two people in the water at 1pm yesterday.

A capsized boat was found about 1km to the south.

An 18-year-old man managed to swim to shore but a search was launched for the other man who was on board.

Marine Area Command Marine Rescue NSW, Surf Life Saving NSW and the Westpac Helicopter spent yesterday afternoon searching.

The search resumed at 8am today, with NSW Police divers also involved.

Part of the boat was pulled from the water about 9.30am.

It has been taken to Port Kembla boat ramp for examination, police said.