The man had been in the waters off Thirteenth Beach in Victoria when he got into trouble just after midday on Sunday, an Ambulance Victoria spokesman said.

Nearby surfers saw what was happening, came to his aid, dragged him back on to the sand, and performed CPR until paramedics arrived.

He was then taken to the Geelong Hospital, where he remained listed in a critical but stable condition on Sunday evening.

Surf Lifesaver Andrew McKinnon said the surfing conditions were difficult at the time.

"It's moving a lot of water at the moment," he told Channel Seven.

"We're getting a bit of wind from the east. It's big. So, there are lots of rips, tides going out."

The incident closed the beach to swimmers and surfers for several hours.