It took more than 50 firefighters to control a blaze that caused extensive damage to a Harvey Norman store in Porirua this morning.

The fire was sparked in a storage area at the rear of the business about 11.14am, Fire Service central communications manager Murray Dunbar said.

It quickly spread into the ceiling and forced the store to be evacuated.

Mr Dunbar said it took 11 appliances to bring the fire under control.