Rescue crews are battling rain and a bumpy swell as the search for a rock fisherman missing from a national park south of Sydney enters its third day.

A multi-agency search resumed on Monday morning for the 71-year-old man, who left his home at Dundas, in western Sydney, on Friday morning to go fishing in the Royal National Park.

Police said the man’s family went to look for him on Saturday after he failed to return home, finding his car in the park that evening.

The man’s family has serious concerns for his welfare as he has a medical condition that needs attention.

A large-scale land and sea search was launched on Sunday involving police and volunteers from the State Emergency Service, Marine Rescue NSW and Surf Life Saving NSW.

Police said the 71-year-old might have been planning to fish at the remote Eagle Rock, located between Wattamolla and Garie beaches in the national park.

Marine Rescue NSW volunteer skipper Brad Whittaker said conditions were poor along the Illawarra coast as the organisation joined lifesavers to search the waters between the two beaches.

“There is one and a half metres of south swell and 15 knots of southerly wind, which is expected to increase across the day,” he said.

“It’s a lumpy swell and it’s raining.”

The missing man is described as being of Asian appearance, 178cm tall with greying hair. He was last seen wearing black track pants and a black parka.

– AAP