Firefighters quickly set up a hose in Mr Hartridge's workshop in case the fire spread.
Plumes of smoke could be seen from the Tauranga expressway as firefighters battled to douse the blaze.
Jason Howell, who was working nearby, said the smoke drifting out from the building was so thick he could not see more than 100 metres down the road.
"It was engulfed in smoke," he said. "I've never seen anything like it. It was pretty bad."
Cold Storage Nelson staff member Gordon Madden saw small flames as he drove past to get lunch and returned to find he could not get back to work as the fire service had cordoned off the street from Cross Rd.
Fire service Bay of Plenty coast area manager Murray Binning said the part of the building that was damaged was a storage facility.
Mr Binning said the front of the single storey building and the mezzanine floor were extensively damaged.
An ambulance was called to treat a volunteer firefighter at the scene but he was not taken to hospital.
It had appeared he was suffering from heat exhaustion but it turned out he had been unwell before he arrived, Mr Binning said.
Fire safety officer Bill Rackham began his investigation into the cause of the fire yesterday but said it was too soon to say what had caused the blaze.