A manager at GAS petrol station said the fire was just across the road from his own business.

"A lot of firefighters are trying to stop the fire but it looks like it's still going."

Another witness said they could see the clouds from the Southern Motorway and went to investigate.

"I can't believe how big it was. I thought it was just a small, contained house fire." 

Five fire engines are in attendance, with two using cranes to battle the blaze from above. 

Vehicles are being turned away from the area, and trains on the Onehunga line have been suspended as the tracks run right behind the building. 

Auckland Transport spokesman Mark Hannan told NZ Herald it was too early to tell if there had been damage to the tracks or if trains would be affected in the morning.