An electrical fault in an external air conditioning unit is suspected to have caused a fire that damaged the Bayfair branch of physiotherapy business Body in Motion.
Two woman joggers passing the Girven Rd rooms raised the alarm at 6.30pm after smelling and seeing smoke pouring out of the wooden building.
Units from Mount Maunganui and Tauranga converged on the scene, with Senior Station Officer Phil Price saying it was lucky the fire was spotted early.
"It could have been a different outcome."
He said flames went under the building, up the inside of the wall and then spread into the ceiling space.
The house was smoke-logged when fire fighters arrived.
While one crew attacked the fire on the outside of the wall, the other crew wearing breathing apparatus entered the house.
Mr Price said they initially had difficulty finding the fire because it was in the ceiling. Mopping up included taking off roofing iron to make sure the fire was fully extinguished.
Most of the damage was restricted to the office on the front left-hand side of the building.
He said it was not hot smoke, so it did not do a lot of damage. The rest of the building would be fine once it was ventilated.