A storage building badly damaged by fire at Tait Communications' Christchurch facility will cost millions of dollars to rebuild.
Dozens of firefighters fought the blaze that started in the office suite at the Wairakei Road building at about 6pm last night.
The cause of the fire is yet to be confirmed.
Tait Communications' chief executive Gary Diack described the fire as "spectacular".
Mr Diack said it had not been established firmly what the cause of the fire was, but two cleaners were in the office suite when it started, fled, and called the fire service.
"It's been reported by the two cleaners who were in building that a light had exploded in the ceiling, but that's yet to be verified by the authorities.
"They were in there, heard an explosion and then activated the emergency response process which resulted in the fire department arriving pretty quickly.
"We're very relieved no-one [was] injured and the emergency response were very very good ... we could have been looking at something much worse and we're not, which is great."
Mr Diack said half of the building would have to be rebuilt, costing millions of dollars.
"It hasn't compromised the whole building, I would have thought, at this stage."
The building was being refurbished after the earthquake for potential sale, and was split into two parts, he said.
While the fire damaged the office suite, the inwards goods storage area only suffered minor smoke damage.
"We're still assessing that, but if there is any impact it'll be very minor and there'll only be smoke damage to componentry that's used in the manufacturing process."
Mr Diack said the fire should not affect the company's manufacturing operation.