Two 17-year-olds lost their lives after flashing flooding tore through the Waitakere ranges.

Two bodies have been recovered near a river crossing in Auckland's Waitakere Ranges after flash flooding on Saturday.

The two were from a group of five that attempted to cross the swollen river beneath the Cascades Falls about 5pm.

One of the group crossed safely; another was airlifted to Waitakere Hospital with moderate injuries, while a third was also taken to hospital with minor injuries.

COLIN ENNOR A flash flood in the Waitakere Ranges claimed the lives of two other walkers who tried to cross a swollen stream.

Nearby, at Kitekite Falls on the Winstone Track, a Canadian firefighter spent hours running up and down tracks to find help for about 20 walkers trapped by flash flooding.

Survivors spoke out about their ordeal on Saturday night, paying tribute to a Vancouver firefighter, Jed, who had helped them to safety.

Jed had been tenting. Despite his fears that the waters had swept away his tent, his passport and everything he owned, he spent hours running up and down tracks to find help for the group.

COLIN ENNOR Auckland man Colin Ennor, his partner Sergio Lopez and their friend Daniel Moises were caught in a flash flood in the Waitakere Ranges that claimed the lives of two other walkers who tried to cross a swollen stream.

'CRAZY WHITE WATER RAPIDS'

Auckland event director Colin Ennor, his partner Sergio Lopez and their two friends were "freaking out" at the torrent.

"The river looked like the Huka Falls – just crazy white water rapids and I think if anyone had walked in, they could not have survived," Ennor said late on Saturday night.

PETER MEECHAM/STUFF Firemen wait for locals to return on Glenesk Rd in Piha after the creek rose rapidly.

When the group finally emerged from the bush, police told them that two others had been swept away.

Ennor said the news made his own ordeal "feel pretty small".

"I hadn't really thought any of us would die out there – but some us were shivering uncontrollably and I'd been worried about hypothermia," he said.

PETER MEECHAM/STUFF The creek on Glenesk Rd in Piha show the effects of the deluge.

New Zealand Mountain Safety Council (MSC) spokesperson Nick Kingstone​ said the groups' ordeals were hugely upsetting.

"This is a tragic and shocking event for the close-knit Waitakere community. Our thoughts are with the families who have now had the worst possible start to their long weekend," Kingstone said.

"We'd like to reinforce our message from earlier this week advising anyone heading into the outdoors this weekend to take extra precautions.

PETER MEECHAM/STUFF A couple of locals walk past a puddle which is all that remains of the flooding on Glenesk Rd in Piha.

"This includes taking care with streams and rivers as they will be up after the last few days rain and may be impassable for some time. If in doubt, stay out: consider finding a new route if necessary."

EVACUATIONS IN PIHA

The flash flooding also caused about 100 people to be evacuated from their homes in Piha, on Auckland's west coast.

STUFF When rain hit Piha on Saturday, residents were shocked at how fast the water rose.

The creek running next to one bach rose by five metres during the deluge, washing water and mud through the building's ground level.

Courtney Walker, 24, was spending the long weekend there with six friends and two dogs. When emergency services recommended they evacuate, the group opted to stay put.

"There was just so much bloody work to do," Walker said. "We had three cars underwater, and needed to rescue our furniture."

She said the creek had been "nice and low and swimmable" that morning, but "went up dramatically" as the rain set in.

Walker said she had never seen the creek flood so quickly before; "in about 10 minutes".

"I actually couldn't believe it and am still stunned," she said.

Flooding had receded by late Saturday evening, leaving the bathroom carpeted with mud and a line of debris scum one metre high around the bach's exterior walls.

Geoff Calvert, who owned Piha Beachstay on Glenesk Rd, said he'd never seen flooding like it: "I've been living here 15 years and that's the worst one that I've ever seen."

About 10 guests who were staying at the property were evacuated onto the road, however got to return later on. Some had chosen to stay with friends for the night because of the flooding.

The house was "fortunately" not damaged, other than the garden needing to be tidied up.

"I'm just glad that everybody's fine, that's the main concern. It was quite an extreme weather event.

WATERS ROSE 'UNBELIEVABLY FAST'

A number of people who were walking in the bush on a track off Piha Rd called police at 5.15pm concerned they were trapped by rising river levels.

The group of about 20 included people from various groups who had been walking in the bush through the afternoon who banded together to get out safely.

They had since found a safe route back out of the bush and were walking out towards Glenesk Rd.

One witness said locals were saying flood waters "rose unbelievably fast"