A man piloting a helicopter carrying three members of his own family has safely made an emergency landing in Sydney's Royal National Park at Bundeena.

The chopper experienced engine failure mid-flight in Sydney's south on Saturday morning.

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The family, including a three-year-old boy, walked away virtually uninjured but had to be winched from the site by the Westpac Lifesaver Rescue Helicopter.

Pilot Peter Butler said the training required to get his pilot's licence became vital when he realised there was an emergency.

"You train and train for these things before CASA [Civil Aviation Safety Authority] will give you a licence and I'm glad they make us do it," he said.

"This is the first time in a long time that I've had any problems and I was very glad I had the training to know what to do.

"You don't get much warning.

"We're very relieved," Mr Butler said when asked how his family were doing.

"We're very well, we're all well."

Mr Butler said he had a very short amount of time to act once he realised there was a malfunction.

"You have to put the aircraft into auto rotation, that's immediately," he said.

"That worked well, we put the aircraft over the ground and as I say we landed successfully with probably minimal damage."

Sorry, this video has expired Young boy rescued after emergency helicopter landing

Pilot did 'really well'

Westpac Rescue Helicopter CEO Stephen Leahy said the landing was "remarkable".

"The pilot has done an incredible job, he's been flying off shore so he's been over water with his family on board," he said.

"He has been able to nurse the helicopter over land and done a very good landing over very thick scrub without injuring anyone.

"He's done really, really well. No person on board the helicopter has been injured.

"They've been assessed by ambulance officers and they're all fine apart from some minor cuts and bruising."

The pilot is being interviewed by police as part of an investigation into what went wrong.