Wates Construction was renovating the grade II-listed six-storey building into offices as part of the £800m Noma redevelopment.
Eight fire engines raced to the former CWS building, near Victoria railway station, when the alarm was raised at around 5.30pm.
Over 50 firefighters battled for four hours to get the high-rise blaze under control, which appears to have destroyed the pitched roof section of the building.
Tram services were halted in the area and electricity supplies were isolated as a precaution.
The view from Hanover Street in #manchester as our platform repositions to fight the blaze. pic.twitter.com/Q8yZmYwfYN
— Manchester Fire (@manchesterfire) October 12, 2015
Here’s some aerial footage from our Air Unit. This infra-red material is invaluable when fighting fires like this. pic.twitter.com/WWMpi0BVvy
— Manchester Fire (@manchesterfire) October 12, 2015
A fire service drone flew over the scene as part of the operation to pick up on heatspots, transmitting images to the ground.
One worker told the Manchester Evening News: “I was working today but left the site at about 4.30pm. I got a call to come back because the building had been on fire.
“Some workers had been carrying out grinding work but we have no idea what has caused the fire.”
A spokesperson for NOMA and Wates Construction said: “We are working closely with the Greater Manchester Fire and Rescue Service and our on-site team to ensure we can gain access to the building as soon and as safely as possible.”