Two members of the public - including an American tourist due to fly home today - braved the treacherous waters of Piha on Auckland's west coast to help rescue two young women.
The alarm was raised yesterday afternoon, when a 19-year-old and a 17-year-old were swept out to sea on the north side of Lion Rock.
Police said conditions at the time were poor, with a king low-tide and large rolling waves, and a strong rip swept the pair up to 200 metres off shore.
Their screams alerted those on the beach.
Two people, including the American tourist, entered the water and dragged the unconscious 19-year-old girl to shore.
The Police Eagle Helicopter landed on the beach and officers performed CPR on the girl for about 15 minutes before the Westpac Rescue Chopper arrived and staff took over.
After "a considerable amount of time", the victim regained a pulse and was flown to Auckland Hospital, where she is still in a serious condition.
The 17-year-old made it back to shore and was treated for shock but was otherwise fine.
Duncan Clarke, who is a lifeguard at Piha and who was off-duty nearby, said he, along with a number of other off-duty lifeguards around, raced to help.
He said the two members of the public who entered the water were heroes.
"I wouldn't recommend anyone do it. I mean, the two people involved are absolute heroes in my eyes," he said.
"But without the knowledge of the beach and the conditions, and the fact that [there] was back-up on the way, it would be something without any rescue equipment that I would've probably second-guessed."
The police said they knew who the tourist who went to the rescue was, but they would also like to thank the second person who helped out.