Three people, clinging to an upturned boat, have been rescued after they were spotted by the crew of the Coastguard Air Patrol.

Nico Doodeman of Coastguard Northern Region said a mayday call was picked up from those aboard the 3.5m plastic dinghy off Orewa Beach, north of Auckland, at 5.29pm.

"The mayday call was picked up on channel 16 saying they were rapidly taking on water and had to abandon the boat pretty quickly," Doodeman said.

"We lost contact with them and so a comprehensive search was launched,"

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Coastguard Air Patrol, two boats from Surf Lifesaving Orewa, a rescue boat from Kawau Island, the police Eagle Helicopter were deployed.

The people were finally located 5km offshore at 6.08pm.

Doodeman said crew in the Coastguard Air Patrol spotted the red fabric from one of the lifejackets.

He credited three on onboard for having the correct safety equipment.

"It was great all three who had been on board were wearing lifejackets and two were also wearing wetsuits," Doodeman said.

"They were prepared with a handheld VHF radio so were able to call for help."

Two of the people were plucked from the water by crew on the surf lifesaving boats and then transferred to the Coastguard boat for a medical check.

The other was pulled straight on to the Coastguard boat.

The three were then delivered to a waiting ambulance on Orewa Beach.

One person was hospitalised with mild to moderate hypothermia.