An unconscious 19-year-old woman was rescued by surfers after being sucked out to sea in a rip at Piha Beach yesterday.
Police said emergency services received several calls that two women had been swept to sea near Lion Rock about 2.20pm.
The women, a 17-year-old and the 19-year-old had gone for a swim, but conditions were "poor" with a king low tide and large waves, police said.
A strong rip swept the women up to 200m from shore, with their screams alerting beachgoers to their distress.
Two men, one an American tourist due to fly home today, entered the water and dragged the women to shore.
The 19-year-old woman was unconscious and officers from the Police Eagle Helicopter performed CPR on her for about 15 minutes before the Westpac Rescue Helicopter team took over.
She regained a pulse after a "considerable amount of time", police said.
Auckland Rescue Helicopter Trust spokeswoman Kerrie Spicer said the woman was flown to hospital in a critical condition.
The members of the public who helped were surfers, she said.
Waitemata Police District Commander Superintendent Bill Searle said the efforts from the public, police and local lifesavers were to be commended.
"Sadly the young lady remains in a serious condition in Auckland Hospital and our thoughts are with her and her family.
"I'd like to thank everyone who was involved in yesterday's rescue, their actions have resulted in her revival at the scene and we now dearly hope she pulls through and makes a full recovery."
Mr Searle said the second person who pulled the woman from the water was yet to be identified.
"We know that one of the rescuers was a tourist here who is on his way home today, but at this stage, we don't have the details of the other person who entered the water and dragged the young lady to safety, please get in touch because we'd like to thank you," he said.