A large fire at a Maui campervan rental facility in South Auckland's Māngere has now been extinguished.
Fire and Emergency northern communications centre manager Daniel Nicholson said emergency services were called to the blaze on Richard Pearse Drive shortly after 5am.
An 80m by 100m workshop was already engulfed in flames when firefighters arrived.
It went to a fifth alarm - the highest alert - and 14 fire appliances and about 70 firefighters were in attendance.
St John Ambulance said four of its vehicles attended the fire but no-one needed treatment.
An ambulance remains on site.
Auckland City area commander Richard Twomey said there were still a few hotspots to dampen down, and this would take a few hours.
He said about 70 percent of the building was destroyed.
Thick, acrid smoke was blanketing a section of Auckland's southern motorway this morning. A light haze of smoke is lingering around the area.
Fire and Emergency advised people in the area to close their windows if the smoke was being blown over, although it was considered low risk.
Auckland Transport said a section of Richard Pearse Drive between Ascot Road and Amelia Earhart Ave has been closed.
Motorists are being warned there's significant delays in the area because of the diversions.
Grant Webster, chief Executive of THL which owns Maui campervans, told Morning Report there was minimal damage to the motorhomes and everyone was safe.
"This was our main Auckland branch, in and around it was our motorhomes, cleaning areas, mechanic bays, our contact centre and most of our Auckland staff are based here."
He confirmed that it appeared the blaze had completely gutted the building.
"It does look the fire has been contained, obviously our focus is on just making sure we've got our crew and equipment ... we'll be contacting customers today."
Webster said he had no clue as to what could have sparked the fire yet.
People at a neighbouring gym were evacuated this morning.
A worker at Fitness 24/7 next door helped to evacuate the six people at the gym.
She said the fire was not threatening the gym but it was coming nearer and was too close for comfort.
RNZ reporter on the scene Matthew Theunissen told Morning Report black smoke was billowing into the air and naked flames were still visible at about 7.30am.
"Firefighters managed to save some of the campervans fortunately the keys were already inside this morning."
There was also some disruption to traffic in the area this morning, he said.
Airport Tyreworx manager Barry Wood, over the road from the blaze, had noticed some flare-ups even after it was contained.
"The people from Maui are out on the street here, they've actually moved a few campervans from the fire so the fire engine can get into the building. They cut the fence so the fire truck can back up into the buildings.
"Basically the whole building ... burnt out now, the whole building is basically gutted out.
"All the offices and workshops are gone."
He said the firefighters were having to be careful because of the LPG canisters in vehicles in the yard.
"There's no other businesses affected, they've attacked it quite well, got it under control pretty quickly."