North Bay Fire and Emergency Services responded to a structure fire at Atlantic Power on Hwy 11 North of the city just before 5 p.m. Tuesday afternoon. (Supplied)

North Bay Fire and Emergency Services responded to a structure fire at Atlantic Power on Hwy 11 North of the city just before 5 p.m. Tuesday afternoon.

A news release from the city Wednesday said Atlantic Power is an electrical generation station not currently in operation.

"Upon arrival, fire crews located a fire in in the walls and roof systems of a generator room," the release said. "Firefighters were able to forcibly open the walls and roof and extinguish the fire that had travelled in many directions behind siding and the roof membrane."

Cause of the fire appears to be conduction of heat from an exhaust chimney to the roof structure and insulation. Fire crews were on scene for about four hours. Damage is estimated at $75,000.