The Fire Service says it was a risky job to bring a large fire in central Christchurch under control.
Eight appliances fought the blaze in a single-storey commercial building on Welles St, between Colombo and Manchester streets, on Sunday morning.
The building was engulfed in flames, sending a thick plume of smoke across the central city.
Senior station officer Michael Balmer says firefighters were faced with a wall of flames when they first reached the scene.
He says there was very poor visibility and the danger of partial roof collapse, which contributed to it being a risky and difficult job.
Mr Balmer says it may have been arson and the fire will be investigated by both the police and the Fire Service.
The affected property is council-owned, having been formerly owned by property developer Dave Henderson. It was being used mainly for storage.
Neighbouring buildings were unaffected.