A teenage boy clung to foliage in fast flowing floodwaters in the Waitākere Ranges for up to two hours before being rescued.
The teen was part of a group of five 17-year-olds who had been swimming near Cascade Falls when heavy rain hit about 4.15pm on Saturday.
They attempted to cross the rising stream to return to their car but as the waters rose only two made it across.
Local teens Sosi Turagaiviu and Mitch Woolley were swept away and died.
A third teen was whisked down stream where he clung to trees and was eventually rescued.
Intensive care paramedic Russell Clark was winched down from the Auckland Westpac Rescue Helicopter to reach the boy about 7.15pm on Saturday.
He said there was a huge amount of rapidly flowing water and when they spotted the survivor, it was obvious his situation was extremely precarious.
"He was waist-deep in fast-flowing water under some foliage.
"He was difficult to see but our pilot Rob managed to spot him and once we got closer we made an assessment and it was pretty evident fairly quickly that we had to rescue this young man. We had grave concerns for his safety."
Mr Clark said the teenager was not moving, and was very cold with multiple abrasions to his chest and back.
"He was very frightened but at the same time there was a sense of relief that someone had actually found him."
The teenager was winched to safety and Mr Clark said he was assuring him throughout the rescue.
"I needed to be quite assertive, and reassured him and said 'you're going to be okay'."
Sosi Turagaiviu and Mitch Woolley were both students in Year 13 at Massey High School.
Principal Glen Denham said they were beautiful boys and the world was a poorer place without them.
"We are heartbroken and in shock," he said.
Waitākere ward councillor Linda Cooper said the school would be reeling from the deaths.
"The Year 13 students have just been on their annual camp to Kai Iwi Lakes, they would've had a fantastic time.
"Boys (are) out enjoying the last bit of summer and this awful accident's happened."
She said it was a freak flood that the boys could not have anticipated.
Auckland Council regional parks manager Rachel Kelleher said a nearby suspension bridge that was washed away in the flood had recently been strengthened.
"The swing bridge that crosses the stream ... it's been there for many, many years and during that time flood waters have occasionally touched the bridge but in this particular instance the bridge was completely destroyed, so that really shows the severity of that event."
Tracks at the Cascade Kauri end of the ranges, including tracks that lead into the area where the boys died, are closed until further notice.
Council staff are reviewing the extent of the damage the storm caused.