Firefighters were battling a blaze at a new £170 million facility being built at Longannet Power Station in Fife on Monday night.
The blaze broke out in an area next to the main power facility where a Flue Gas Desulphurisation Unit - a facility that will help capture sulphur gases - is currently being constructed.
It was thought a filter inside an air heater may have caught alight, resulting in a small fire.
Fife Fire and Rescue said they called out at 3.05pm and sent three engines and an aerial platform to try and put out the flames.
On Monday night they were still at the scene of the blaze, which had been brought under control.
Fife Police sent six officers to the scene to assist and said onsite workers had initially managed to douse the flames but they had to call in the fire brigade after the fire restarted and set a building alight.
A spokesman for ScottishPower, who run Longannet, said that the circumstances surrounding the initial blaze are now under investigation.
He added: "The fire didn't affect output at the station and there were no injuries. The causes of the fire and the resulting damage will be investigated in the coming days."