Three New South Wales fishermen have died in waters off South Australia’s Limestone Coast, SA Police say.

Police said the alarm was raised about 2:30pm on Sunday, when the three men did not return to shore at Beachport in the state’s south-east.

A search was launched with the combined efforts of police’s Water Operations, PolAir, the State Emergency Service, local boaties, and other aerial assets, including drones.

Three fishermen have died in waters off Beachport in South Australia's south-east.  (ABC News: Sam Bradbrook)

Police said the men, aged 65, 67 and 74, were found dead and their bodies were recovered.

Officer-in-charge of Limestone Coast region, Superintendent Trent Cox, said the trio did not appear to be wearing life jackets on the 6.7-metre vessel.

“From what we can gather, there were life jackets aboard, sadly it does not appear any of the gentlemen were wearing them,” he told ABC South East SA.

“One death is a tragedy but three is unthinkable.

“They’ve made a poor decision to go out there and paid the ultimate price unfortunately.”

Members of the public have been asked not to collect debris from the boat and instead to leave in situ for police to collect.

“Members of the public trying to do the right thing may interfere with crucial evidence that leads to identification of how this incident might have happened,” Superintendent Cox said.

Local fisher Alan Campbell told ABC South East SA he tried to warn the men about rough conditions a day earlier.

“I said, ‘mate, however big your boat is, there’s a wave to match it and these aren’t the conditions to be out in that boat’,” Mr Campbell said.

 “When I saw the trailer on the ramp, I was very concerned.

“Before I rang the police, I drove around the beach … but I couldn’t see anything.”

Mr Campbell then raised the alarm with authorities.

Beachport Tavern manager Charan Muduganti said he saw emergency services and locals attend the boat ramp yesterday afternoon to try and find the men.

“Lot of boaties want to help them out … but it’s kind of rough weather yesterday,” he said.

“I had a little hope they would be somewhere alive, but, yeah, it’s so sad.”

Mr Muduganti said many locals chose not to head out to sea yesterday due to rough conditions.

“It was really rough weather, very high tides, very high waves and it was really windy, that’s the worst part,” he said.

Police will prepare a report for the coroner.