Police suspect an arsonist may be behind the razing of a vacant house at Buranda early this morning, just hours before it was due to be demolished by contractors.

A passing motorists alerted authorities after spotting fire in the raised wooden Queenslander on Ipswich Road at Buranda, south of the city, about 2.30am.

By the time emergency crews arrived the structure was totally engulfed in flames, forcing the closue of one lane of Ipswich Road.

Forensic investigators are now picking through the charred rubble for clues about how the fire started.

A police spokeswoman confirmed the house had been vacant for a number of years and the power had been cut. It had been due for demolition today.

Firefighters spoke to the building's owner at the secen and police are treating the matter as suspicious.