Videos posted to Facebook show an entire wall torn off from a what appeared to be the Elite Bathroomware Showroom on Allens Rd in East Tamaki on Saturday.
The footage showed metal sheeting and wood strewn together with what looked like computers and office equipment.
An ambulance in which a woman was giving birth was also reportedly hit during the tornado.
Falling branches slammed into the ambulance that was parked in a residential driveway blowing out the windows, reporters at the scene were told.
Dally said there were reports of major structural damage to other industrial buildings.
However, there were no reports of injuries.
Phillip Boughey was enjoying his morning at home when he opened his curtains and saw the tornado about 1km away. He grabbed his iPhone and raced off to film it.
From a distance, he could see the tornado picking up and tossing debris. Once he got to the scene, on Allens Rd, several buildings had been damaged.
People were inside Elite Bathroomware when the tornado hit, he said.
"They've got quite a few staff in now and electricians making sure the wires are safe," he said.
Residents in Dairy Flat reported seeing a small tornado whip through streets about 11pm yesterday.
Trees and a trampoline slammed against Bianca Paterson's house while her children screamed.
She said her house escaped serious damage, but the tornado wreaked havoc in her garden, dented her roof with debris, popped manhole covers open and cut power and water supply to her house. She woke up when it picked up the trampoline.
"It smashed into the side of our house, and then it just flew up onto the roof and just smashed on the roof. It took out our massive commercial playground, it was just so loud. And then, all of a sudden after a minute or two, it was all over.
"Devastation was left behind and if you look outside our property, there's just a trail - all these big beautiful old trees, they've just been cut in half or demolished."
Thunderstorms delivered 49mm of rain from midnight to 1am on Saturday in parts of Auckland.
In the same hour, MetService said the Skytower recorded a base wind speed of about 75km/h.
It prompted 24 weather-related callouts for Fire and Emergency crews, handling incidents including flooding, lifted roofs and toppled trees and powerlines.
Auckland Council said it was not aware of any serious damage.
MetService meteorologist Alwyn Bakker said 49mm is an intense burst of rainfall in a short space of time.
"So that is in the downpour territory. There would almost certainly have been some flooding.
"That is an awful lot of water to come out of the sky in just an hour."
MetService said most of the wet weather has passed through Auckland.
However, the New Zealand Transport Agency advised earlier this morning that due to flooding, a detour is in place on the State Highway 1's northern motorway. The Oteha Valley Rd southbound on-ramp is closed.
- NZ Herald and RNZ
