A Christchurch factory is back in business just two days after a spectacular fire.

The blaze damaged the roofs of four storage buildings at the Ravensdown site in Hornby.

Early indications suggest a spark from a welder landing on rubber conveyor belt started the fire.

CEO Greg Campbell said finished product is intact and the quality hasn't been compromised.

"We are asking customers and transporters to give us a bit of breathing space while we iron it out and get back to normal operation."

He said the amount of people offering support and well wishes has been humbling.

The exact cost of the damage was not yet known but it is expected to be a multimillion-dollar fit out.