Emergency services were called after the 45-year-old became caught in a rip at Bongola Beach, south of Narooma, about 1.30pm on New Year's Day.
When lifesavers arrived at the scene, onlookers told them the man went into the ocean to rescue a 14-year-old boy, but after saving the teen he disappeared under water, Surf Life Saving NSW chief executive Steven Pearce said.
A helicopter sent from Moruya spotted the man who was pulled from the rip by lifesavers, but paramedics couldn't revive him and he died at the scene.
"It's a really, really tragic incident and we have numerous cases each year ... where someone goes into the rescue and they, in turn, become the victim and the person they went to rescue successfully escapes the rip they were caught in," Mr Pearce told AAP.
NSW Police confirmed the man who died was an off-duty officer. Local police will prepare a report for the coroner.
With warm temperatures driving thousands of people to the state's beaches this summer, NSW lifesavers have already carried out more than 1000 rescues since Christmas, which is a record.
"We've never ever seen this before," Mr Pearce said.
"So the primary message today, particularly because it's such a bumper day for the beach is: we're urging people to go to a patrolled location, and that's anywhere with a red and yellow flag flying and where our lifesavers, and our lifeguards, are on duty."
13°C