George Kalajzich, Dax Cairncross and Lucas Mak, all aged 15, had finished school for the day, were hanging out at the beach and checking out the waves wondering if they should go for a surf.

It was like any other afternoon, until it wasn't.

READ ALSO:

It was 6.45pm on Tuesday and they spotted someone stuck in a rip and heading out to sea, as another person struggled back to shore from that same rip.

"One of his mates came running towards us asking for help," Dax said.

The person stuck in the rip was a 17-year-old Sydneysider who was in Kiama for schoolies week. He was around 100 metres out to sea.

"He was just trying to keep himself above water," George said. "His mates were a bit frantic on the shore."

The Sydneysider wasn't a strong swimmer so George bolted 300 metres up the road to his house, grabbed a surfboard and rushed back.

Lucas paddled the board out to the struggling swimmer while George swam behind.

"He was gasping for air and trying to get on the board as quickly as possible. He kept saying thank you," Lucas said.

Clutching onto the surfboard with one hand and paddling with the other, Lucas and George brought the schoolie back to shore as he lay gasping on the board.

"We didn't realise how bad it was at the time," George said. Paramedics treated both 17-year-old Sydney teens on the sand and then rushed them to Shellharbour Hospital. They were assessed but not admitted for treatment.

In the wake of the dramatic rescue, and adoration from their teachers and classmates, the Kiama teens are taking it all in their stride.

"We'll just keep surfing I guess," George said.

Dax's father, former Ironman Drew Cairncross, said the Kiama teens are all competent in the water.

"It was good for them to problem solve and it sounded like they figured out the right solution," he said.

"They've been surfing, fishing their whole lives down here. They're always in the water."

George's father, Todd Kalajzich, is extremely proud of his son and his mates.

"You worry about your kids but when they rescue another kid you think 'they've got this'," he said.

The Kiama teens were nippers at Kiama Downs Surf Club when they were young and club president Steven Guy praised them for the rescue. The visiting teens were swimming in the "only rip on the beach".

"They were really nice kids, they hadn't been drinking, they just didn't know the beach," he said.

Shellharbour Council lifeguard Craig Bowley urged people to only swim during patrolled hours.

"We have some beautiful beaches along our coast, but also some very dangerous ones, such as South Bombo," he said.

"Please remember the most basic rule, no flags means no swimming."