'Shaken and upset': Tense moment dad and daughter found clinging to capsized catamaran

A distressed teenage girl and her father who survived an overturned catamaran that killed three people in rough seas off Newcastle are set to be released from hospital.

The 16-year-old and 50-year-old man were found clinging for their lives when authorities reached the boat about 13 nautical miles off Stockton Beach on Thursday morning.

They were winched from the water and taken to John Hunter Hospital to be treated for hypothermia.

The girl's 78-year-old grandmother and grandfather, from Glenhaven in Sydney's northwest, did not survive. Their male friend, who was living on the Central Coast, also died.

The three bodies were eventually retrieved by Marine Rescue.

The 11.7-metre catamaran had left Shoal Bay earlier on Thursday and was heading south towards Ettalong Beach on the Central Coast.

Westpac Rescue Helicopter pilot Graeme Anderson said the girl and her father were left shaken by the incident.

"The conditions out there were really really poor. Strong winds, large waves. We were lucky that we got there to get them," he told Nine's Today Show on Friday.

"They were shaken and very upset.

"They were suffering hypothermia and a slight knock to the head from bashing up against the vessel, but they're very stable and I believe they may be going home today."

Detective Acting Superintendent Grant Healey said it was unclear how the boat capsized, with police yet to properly speak with the survivors.

"Our detectives spoke to them last night and they were very distressed," he told Seven's Sunrise.

"We're going to see them today."

Authorities say all five people were wearing life jackets.

A strong wind warning had been issued for the region, and remains in place for the Hunter, Macquarie, Sydney, Illawarra and Batemans Bay on Friday.

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