Two people are dead after being swept away in a swollen river in the Waitakere Ranges.
About 100 people have also been evacuated in Piha tonight, up to 20 people were stranded on a nearby walking track due to rising waters and 50 are stranded at a wedding venue on Bethells Rd.
Police said five people got into trouble crossing a river about 5.15pm near Cascade Falls. One made it across but three were swept away and remain missing.
One person was rescued and transported to Waitakere Hospital in a moderate condition.
Another man who earlier made it to safety was also taken to hospital with minor injuries.
The fifth person involved was uninjured.
"Police are working to establish if the bodies located are part of this group."
Rescue helicopters responded to the scene as a major search and rescue operation got underway.
A man from the Waitakere Golf Club on Falls Rd, who did not wish to be named, said emergency crews were looking for the missing people near Cascade Falls.
He said there were two fire trucks, two ambulances and a police car in the area.
He said the rain was "severe" between 4pm and 5pm.
President of the Auckland Tramping Club Tony Walton said people should not cross a river if they can't see the bottom of it of if the water is running faster than walking pace.
"If it's a swollen river you just don't go crossing it."
Walton said flood waters can be very strong and very fast.
He advised people to stop and think before crossing any river.
Piha evacuations after deluge
Police and fire are evacuating about 100 people from homes in Piha around Glenesk, Seaview and Beach Valley Rds.
People are being evacuated to the nearby surf club or campground as a
A police spokesperson said the flooding looked to be receding and, if it continued to do so, police hope to allow people back into their homes within a couple of hours.
Earlier, Fire and Emergency northern shift communications manager Scott Osmond said people were being evacuated from Glenesk Rd.
"Five or six houses are at risk of flooding, so we're evacuating as a precaution."
Osmond said water levels in a nearby creek were rising, due to the heavy rain.
A local campground said a member of their staff was speaking with authorities and they were now waiting to hear from authorities about how they can help those affected.
A worker at the Piha Store said they had seen fire trucks and heard loud sirens in the past hour or so and assumed there had been a fire in the area.
A worker at the Piha Surf Shop, which is elevated, said they could see "a lot'' of water down below, following a sudden extreme period of heavy rain this afternoon.
"The flooding is in the valley. My son said there is water over the road at the fire station and the road has been cut off.''
The Piha Fire Station is on Seaview Rd, near Glenesk Rd.
Talking about the weather, the woman said they had had some warning just before conditions turned "extreme".
Piha resident Bevan Hill said the local art gallery was flooded as well as the campground.
"There's a lot of people there saying they've never seen anything like it before.
"The river coming out on Piha beach is incredible. It's like the Waikato River flowing out there."
Hill said there was "water everywhere" and he had water coming in his front door on Garden Rd earlier, but was now safe.
There were "a lot of wet and soggy campers" packing items into their cars, and a few tents had ended up underwater.
"It all happened so quickly, too."
Several members of a church youth group holidaying at a Piha campground were among those to be evacuated.
A woman who asked not to be named said the floodwaters came in within a matter of just a few minutes after a flash of bad weather.
"Not long after thunderstorms, we saw campground staff walking around outside looking across the grass - we thought they were looking for something.
"All of a sudden we looked up to see all this water just flooding towards us. It was so fast - it carried down logs and just flashed the whole ground in about two minutes.
"It just happened so fast, we literally just picked ourselves up and got out."
Teen Gideon Hope, 16, said they had just finished afternoon devotion when the waters started flooding into the hall he was in.
"The water just came in, we couldn't do anything about it.
"It was a bit scary," the 16-year-old, from Henderson, said.
Others said the water reached their ankles.
The woman who spoke to the Herald said she had heard flooding was worse at the intersection of Glenesk and Seaview Rds, where a number of cars were lifted at one point by the floods.
Phil Wallis from the Piha Surf School said he was in the water taking a lesson when the rain started.
"It was horizontal . . . in almost 40 years here it's the strongest rain in a short period I've seen. You couldn't see the beach.
"Immediately the stream stuff started just pumping out brown water."
A nearby stream which usually didn't have any flowing water when there had been little rain transformed into a "torrent".
"It was almost a standing wave coming down the beach."
The Piha Surf Lifesaving Club were among those to help following the flooding; with members being called out to help residents whose vehicles had become stranded as a result of floodwaters.
A number of residents were brought back to the club for a short time, where they got to have a meal and a cup of tea before heading back home.
Club president Peter Brown said: "We've has flooding at Piha before, but not of this intensity.
"It was just really a very short 30 minute huge amount of heavy rain."
Debbie Leigh from the Piha RSA said people were reporting cars drifting in the flood waters.
Wallis said friends of his had taken pictures of cars floating in floodwaters, with the water rising up to the sills inside the cars.
Bushwalkers concerned by river levels
A number of people who were walking in the bush on Winstone Track off Piha Rd
called police at 5.15pm concerned they were trapped by rising river levels.
The group of approximately 20 people included people from various groups who
had been walking in the bush through the afternoon and banded together to get
They have since found a safe route back out of the bush and are currently
walking out towards Glenesk Rd.
Julia Woodhouse at the Black Sands Lodge in Piha said she couldn't see any flooding where she was, but she had to go and dig out the stormwater drain to get rid of surface flooding on the road.
Woodhouse digs out the stormwater drain herself every time there is a storm.
The lodge had some surface flooding coming down the driveway from the road, but nothing serious.
"During the storm it was just extraordinary.
"We're actually at one of the lowest points [of the road]. We've been very fortunate."
The lodge is on Sylvan Glade.
Trapped at wedding venue
Fifty people were at a wedding venue on Bethells Rd when floodwaters started rising.
A police spokesperson said the group were at a wedding reception at Flaxmere House.
Police and fire crews attended the venue but were not required as the water started to receed.
The group were not believed to be in any danger.
A serious crash has also occurred near Waitakere. A Herald reporter said a vehicle was on its roof. Emergency services were yet to reach the scene but people in fluro vests were directing traffic.
MetService meteorologist Brian Mercer said heavy rain and thunderstorms were expected to continue over Auckland this evening.
He said the wild weather was caused by a low pressure system, which was centred north of Helensville about 6pm. The system was tracking up the country which would see the heavy rain ease by midnight.
A heavy rain watch was in place for Auckland, Northland south of Whangarei, Great Barrier Island and Coromandel Peninsula until midnight.