Emergency services were sent to the scene in Moray Road in the Aberdeenshire town after the alarm was raised shortly after noon on Friday.
The Scottish Fire and Rescue Service (SFRS) said the property appears to have suffered substantial damage.
A man was taken to Aberdeen Royal Infirmary with injuries that are not thought to be life-threatening.
Police said they were called at 12.10pm to reports of an explosion.
A Police Scotland spokesman said: "Police were called around 12.10pm on Friday, following the report of an explosion at a block of flats on Moray Road at Watermill Road, Fraserburgh.
"Police and fire service units are currently dealing with the incident which appears to be the result of a gas explosion.
"A man has been taken by ambulance to Aberdeen Royal Infirmary where his injuries are not believed to be life-threatening.
"There are currently no suspicious circumstances and Moray Road will remain closed between Watermill Road and Kinnaird Road for some time."
A spokesman for gas distribution network SGN said: "We were called to a property in Moray Road, Fraserburgh, by the emergency services at around midday following reports of an explosion.
"Our engineers have made safe, carried out safety checks and left the site at around 2.30pm. The incident was not related to our gas network."