A disused office building in the centre of Preston was deliberately set alight this morning, say fire services.
Three crews from Preston and Penwortham were called to the incident on Pole Street at around 7.40am.
On arrival crews found a number of tyres on fire on stairs leading to the basement of the building.
A spokesman said: "We were obviously concerned that a homeless person may have been in the basement but we used thermal imaging cameras to make sure that was not the case.
"We extinguished the fire using a hose and cleared the building of smoke using a positive pressure ventilation unit."
The fire is being investigated by police and fire services.
Nobody was injured during the incident.