An 18-year-old schoolboy drowned at Muriwai while trying to save the life of a classmate.

The accident was followed by the suspected drowning of a 15-year-old boy at Piha on Sunday. Searchers were still trying yesterday to find the younger boy's body.

Neither teenager had been named last night.

The older boy died while going to the aid of a female classmate who got into trouble in the water at Muriwai about 2.30pm on Friday.

He is believed to have been a Year 13 student who was on a geography field trip from Tangaroa College in Otara, Manukau City.

Tangaroa principal Ngaire Ashmore did not return phone calls yesterday.

The Herald understands staff at the college have been told not to speak to the media.

A surfer spoke yesterday of how he had just finished surfing at Muriwai when a group of Pacific boys began shouting at him to help their friend.

"I could see a girl floating out of her depth and so I swam out there and when I got there, she was still floating and shouting for help and there was this other guy face down in the water.

"I got the girl to go on my board and then I was trying to pull the guy up on to the board so that his head was out of the water and I was struggling with that because he was quite heavy."

The man said his brother and a woman surfer swam out to help him.

"We managed to get him on to one of the boards and we swam into shore with him and the girl."

CPR was performed on the boy and the Westpac rescue helicopter flew him, still unconscious, to Auckland City Hospital. He survived until Sunday, when his family made the decision to turn off his life support.

The surfer said the tide was out and conditions "weren't that rough", but the beach drops off quite suddenly.