Tuna fishers Conor and Nicky Edwards and Luke Goldstein, in their early 20s from Melbourne, were fishing near Portland, Victoria, from their boat when they learned an emergency beacon had activated.

Nicky and Luke, who work up to four months of the year in Portland with Reel Time Fishing Charters, then received a call from a fellow skipper who gave the co-ordinates of a jet ski rider they said was in trouble.

Meanwhile, emergency services dispatched the coast guard and a police airwing, but it was the young fishers who raced to the scene and rescued the 30-year-old Thomastown man about six kilometres offshore.

"When we got him his lips were blue from the cold. He didn't have the energy to climb into the boat so we had to pull him in," Conor said.

The anglers drove past the man after mistaking him for his Esky adrift about 200 metres away.

"You couldn't really see him because of the swell of the waves. You could barely see the jet ski," Nicky said.

Conor said the man told him he was hooking a fish when his jet ski started taking on dangerous amounts of water.

"The jet ski started going under and a wave hit him and it rolled over," he said. "Every time he would try and flip upright it would just keep rolling again.

"It was much better than we thought it could have been. It didn't sound like it was going to end too well."

Portland police expressed pride that the city's local anglers were all "very well equipped and look out for each other" following the incident.

Nicky said the man told the anglers he'd been in the water for about an hour and a half before they reached him.

They gave him clothes, water and towed his jet ski ashore. He later went to hospital in a stable condition.

"We did well to find him. It was like looking for a needle in a hay stack," Nicky said. "He said 'I've never been so grateful to see a boat in all my life'.