Initial reports of the incident were received at 05:55 BST this morning, by which time the fire had already taken hold of the commercially-used building on all its floors.
The fire has also spread to an adjacent building and led to nearby streets being closed to the public.
Early reports suggested that a number of homeless people were in the building during the fire but police have attempted to allay such fears.
"There is not believed to have been anyone trapped in the building," a spokesperson for Greater Manchester police said.
"Adjacent buildings have been evacuated and everyone has been removed from the area safely."
But the primary effort of firefighters at the scene remains preventing the five-storey building from collapsing. Emergency scaffolding has been erected around the external walls, which are believed to be the only part of its structure still standing.
The fire and subsequent closure of streets have led to substantial disruption within the city centre.
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