Police and fire experts are investigating a blaze at a ground floor flat in Blackpool.
The property in Branstree Road, Mereside, was cordoned off as a crime scene after the incident early today.
Detectives and a fire investigation officer were at the property which suffered severe damage.
Three crews, two from Blackpool and one from South Shore, raced to the scene at around 4.45am after reports someone may be trapped in the premises.
Firefighters wearing breathing apparatus conducted a search of the flat, but no-one was found.
Watch manager Tom Ashworth, from Blackpool Fire Station, said: “We got the call that there might be someone in the property.
“When we arrived at the premises the front door was well alight. But after a thorough search we established there was no-one in the flat.
“We are treating the fire as suspicious. A fire investigation officer is at the scene.
“The property has been cordoned off and we are treating it as a crime scene while we carry out a full investigation.
“The flat suffered severe damage by fire, smoke and heat. We can’t say at this stage what caused it.”