Fire fighters are investigating the cause of a fire that saw workers run for their lives, and a city motorway closed during rush hour as fire gutted an Onehunga warehouse last night.
Health inspectors are to check the building, built in the 1960s, to see if it was safe for fire safety officers to go inside and begin the search for clues about the cause.
The Health Department would collect samples from the building, which was originally used to make jandals, fire safety officer Russell Dickson said.
A team of fire safety officers would be at the scene but would not go into the building unless it was safe.
"As far as the cause all bets are off. I am not about to speculate," he said.
Northern fire communications shift manager Megan Ruru said fire fighters were on stand-by overnight.
More than 80 firefighters in 20 fire engines battled the blaze, which left the Mitre 10 Home and Trade shop in Princes St a heap of timber and ash, and forced the evacuation of neighbouring factories.
The fire cut electricity to surrounding households and businesses but lines company spokeswoman - Phillipa White from Vector - said power had been restored to the area by 2.50am.
She said some areas are having their power supplied by generators because of extensive power damage to the network.
Ms White said at the height of the outage there were 579 customers affected.
The plume of smoke from the fire could be seen from as far away as the North Shore, and traffic to nearby Auckland International Airport was delayed up to 40 minutes.
The Southwestern Motorway - a major thoroughfare to the airport - was shut between 6pm and 7pm.
Firefighters were still struggling to control the blaze more than three hours after it started, and were expected to stay at the scene overnight.
Northern fire communications shift manager Jaron Phillips said the fire had spread to three adjacent buildings. The 50m x 30m warehouse was engulfed in flames when firefighters arrived.
Reports of downed power lines, power lines on fire and transformers on fire were received from the surrounding area.
The chief fire officer at the scene, Larry Cocker, told TV3's Campbell Live programme the store was filled with tents, gas burners, camping gear and plastic tables.
"It's an old building, the fire was rapidly spreading through the complex, the roof was exploding off and it was underneath high-tension wires.
"We had a separate fire at a transformer at another street, so we had a number of things on the go all at once."
Freeman Davey, who works at the Grove Mitre 10 store opposite the main Mitre 10, said staff were seen running from the store after several explosions went off.
"It happened really fast - the fire escalated really quick. We went out and there were bits of timber and pipe flying out from the roof.
"There was heaps of banging - really big bangs. There's lots of gas bottles in there - one of them must've gone off."
Electricity to houses on neighbouring streets and businesses was cut.
Vinod Narayan, who works on neighbouring Church St, said he realised something was wrong when the electricity suddenly went out.
"The power went off and when we looked outside, we saw a police car going past really fast. We climbed the roof to see what happened and we saw the smoke and the flames - just a massive fire," he said.
The man who discovered the fire, customer Brent Morrissey, told Newstalk ZB he was alerted when he smelled plastic burning.
"It seemed to get strong very quickly and I turned around and the wall at the side of the building was on fire."
When he saw flames, he started yelling at staff to leave the store.
Police blocked the Southwestern Motorway between Hillsborough Road and Coronation Road for two hours from about 5pm.
Earlier yesterday, a major gas leak in the west Auckland suburb of New Lynn led to the evacuation of several buildings and closed streets including Rankin Avenue, Clark St, Veronica St and Great North Road.
Ms White said 32 homes and businesses were still without gas but should be restored later today.
Rail agency Ontrack closed the western line between Avondale and Henderson replacing trains with bus shuttle services last night but trains are now running as normal.
The agency has yet to determine whether the gas leak was caused by work on a $160 million railway trench, although an official said the ruptured main was close to the rail corridor.