Five fire crews are tackling a blaze at a top floor flat in Chain Street in Bradford city centre.
The blaze broke out shortly after 11.30am when smoke was seen billowing from the roof of the building. Three ambulances also attended the scene with at least one person taken to hospital for treatment.
The aerial appliance brought the smoke under control at about 12.30pm but clear damage could be seen to the roof and back of the flat.
The cause of the fire is as yet unknown and fire investigators and police are in attendance.