Services were called to the scene at Square Road in the town centre shortly after 3am following reports of a fire at the four-storey building.
The building, at the junction with Church Street, is a former mill which has been converted into retail units, and is opposite the entrance to Halifax Central Library and the Piece Hall.
West Yorkshire Fire & Rescue Service said the building was 40% involved in fire, although have not reported any injuries.
Six fire engines from different stations across the brigade are in attendance, two of which are using aerial platforms to extinguish the fire. Specialist officers and supporting resources are also in attendance.
A spokesman for the fire service said "early arrival has ensured information could be collected from witnesses to get the investigation into this fire off to a good start".
Square Road remains closed while services deal with the fire.
UPDATE: West Yorkshire Fire Service have said the fire is now out.
A spokesman said: "Stopping such a well developed fire in this type of building is quite a feat. Well done to all fire fighting crews in attendance."