The trio, aged 25, 40 and 45, were rescued after clinging to a life raft for around half an hour, before they were winched to safety by a NSW Ambulance rescue helicopter crew.

The crew had been on the water for a few days after travelling in their 22-metre tuna trawler, Sensation, from Coffs Harbour down to Ulladulla, where it is registered.

Around 7.30am, the three crew members reported to Marine Area Command that they were preparing to activate their EPIRB (Emergency Position Indicating Radio Beacon) and abandon ship as it was going under.

Vessels from Marine Rescue Shellharbour and NSW Police Force immediately responded, along with the rescue helicopter.

"The winds were 30 to 40 knots from the west and the seas were choppy with about two metre swell," Marine Area Command's Sergeant Sean Netting said.

The helicopter touched down at Tom Willoughby Oval, Shellharbour, just after 9am.

The men, who were cold but uninjured, were treated by NSW Ambulance specialist crews.

"They weren't in the water long so they were all fit and healthy," Sgt Netting said. "They were happy to be alive and out of the water.

"They were in the water for only about half an hour so it wasn't too traumatic for them. They were just cold.

"They did everything right. They are commercial fisherman who knew what to do.

"They waited until the boat was just about to sink before entering the life raft and they were rescued very quickly."

NSW Ambulance Inspector Matt Sterling said any ocean rescue was a challenge and it wouldn't have been possible without the service's specialist medical teams who did an "excellent job".

"These three men are very lucky to be alive ... luckily we got to them in the nick of time," he said.

"... The vessel was sinking quite quickly and they had to evacuate.

"When we arrived with our two helicopter resources out to sea we found the three people in a life raft, uninjured fortunately.

"We've extracted them via winch up to the helicopter and have returned them to a location back on shore where they've been assessed and fortunately no injuries have been identified."

Inspector Sterling also applauded the efforts of the crew members.

"The vessel was well equipped with the appropriate emergency response equipment, they activated early and they passed the distress call to local police and maritime as an early indication they required assistance and we were able to get them in a timely manner," he said.

Sgt Netting said the captain was not sure what caused the trawler to start taking on water and the cause was likely to become clearer following investigations.

"They heard a noise and went to investigate, within minutes the engine room was full of water," he said.

"They took steps to raise the alarm. They rang the boat owner who called police, who were there within minutes.

"They claimed to do everything they could to stop it sinking including using additional pumps but it was overcome by water."

Sgt Netting said the boat sunk 250 metres below the surface where it would remain, becoming "reef for fish".

Vessel owner Joe Lagana said his crew were safe, which was his main concern, but he could not discuss further.

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