People scrambled to save what they could as "massive amounts" of floodwater hit parts of West Auckland, with 200mm of rain in Kumeū overnight.
Homes were flooded and people had to be rescued from their cars. Emergency services have dealt with 370 calls for assistance.
Kumeū's main road and many of its shops are under water, houses are damaged and cars are submerged.
Kumeū Ratepayers Association chair Guy Wishart told Nine to Noon the speed of the flooding was devastating. He hadn't been able to get out of his house, with a "massive load of water" making its way down from higher ground to the flood plain.
NIWA meteorologist Ben Noll said Kumeū experienced its second-wettest day on record, and had 149 percent of the normal August monthly rainfall in a single day. Records in the region date back to 1943.
Gerry Fennelly, who lives in Henderson Valley, told Morning Report he woke shortly after midnight to almost a metre of water coming up to the house and underneath it. Fennelly said it was like a wave coming up the road and carrying logs with it. "It was terrifying", he said.
Here's how it unfolded: