The moment a surviving Waitakere teen was winched to safety

Dramatic footage shows the moment a teenager was winched to safety by heroic rescuers after a storm surge in the Waitakere Ranges.

A group of five friends had been swimming in a stream when flash flooding swept three of them away. In a matter of minutes a summer adventure at a west Auckland swimming spot had turned into a fight for life that ended in a double tragedy.

The group tried to cross the river; two made it to safety, but three were swept away.

Mitch Woolley and Sosi Turagaiviu, both 17, were swept to their deaths.

One of their friends, who was also swept down river, was winched to safety after clinging to a tree for nearly three hours.

Cold, wet, exhausted and wearing just a pair of shorts, he suffered only moderate injuries and was able to walk to a waiting ambulance.

"The young men... tried to get on some rocks, on one side of the stream; however, the water continued to rise and became very rough," said Inspector Fata Willi Fanene on Sunday afternoon. 

Insp Fanene said it had been "a very traumatic experience for them and their families". 

"An incident like this is an awful reminder of the power and unpredictability of our natural environment." 

The deaths have been referred to the coroner.