Two fire crews attended a call to a property in Brassey Rd around 4.15pm on Wednesday.
Senior station officer Jes Sorensen said there was a small fire on the inside of the villa roof which burned out some of the wood structure.
"It had been smouldering for a while and we believe it may have been caused by a spark from the chimney flue," Mr Sorensen said.
Crews were also called to Whanganui Hospital on Wednesday after a fire in a toaster in a staff kitchen area caused a smoke nuisance. The fire was extinguished before fire crews arrived.