Chopper forced down in Sydney's south

A family of four has escaped virtually unscathed after their helicopter was forced to make an emergency landing in thick scrub near a southern Sydney beach.

The pilot was flying his three-year-old grandson and the boy's parents along the coast near Bundeena when an engine malfunction forced him to put the chopper down quickly in dense bushland in the Royal National Park just after 10am on Saturday.

The Westpac Lifesaver Helicopter was called to the landing site where the scrub was so dense a rescuer was forced onto his hands and knees to reach the family.

"We found that they had only minimal cuts. They were all in good health but they were obviously shaken as a result of an unforeseen crash," Westpac Lifesaver spokesman Stephen Leahy told AAP, adding that the pilot did a "magnificent job" of landing.

"They were very lucky indeed considering the thick scrub they were forced to land in. The pilot identified the malfunction very quickly and has taken every precaution to land safely."

All four were winched out separately to Bundeena, where they were assessed by paramedics.

It is understood the pilot was then interviewed by local police investigating the circumstances surrounding the incident.