A fire has caused $800,000 damage to a Port Kennedy family business.

The blaze on Blackburn Drive started just before 7pm on Tuesday. More than 30 firefighters attended and brought the fire under control within 90 minutes.

A Department of Fire and Emergency Services spokesperson said the cause of the fire had not been determined, but it is believed a door was left open and the fire spread quickly through the building.

Fire investigators will be at the scene throughout the day in an effort to determine the cause of the fire.