The cause of the Halifax mill fire in the town centre is already underway West Yorkshire Fire and Rescue Service has confirmed.
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 were called to Square Road in Halifax in the early hours of this morning.
Two aerial platforms were also used 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".
Keep up-to-date with all the latest news and breaking incidents in Halifax - join our dedicated Facebook group here.