Police are working to the theory several suspicious blazes lit in Singleton this week are linked.
About 11:25pm on Monday, October 4, police attended two grass fires near John Street, and a short time later, another grass fire was located in the Darlington and Singleton Heights area.
The fires were extinguished by Fire & Rescue NSW.
About 12.15am on Tuesday, emergency services were called to the corner of Market Street and Patrick Street at Singleton, following reports of a building fire.
Fire & Rescue NSW crews doused the blaze, which destroyed one building and seriously damaged another.
Both buildings were unoccupied at the time and there were no reports of injury.
Officers from Hunter Valley Police District attended and established a crime scene.
The fires are being treated as suspicious and initial inquiries suggest they may be linked.
As investigations continue, police are urging anyone with information to come forward.