People were evacuated from a unit in Newhall Road, Newhall, when a fire broke out in the roof cavity at about 8am.
Five fire engines from Sheffield Central, Parkway and Elm Lane stations and a turntable ladder have been dispatched to the site.
A fire service spokesperson said earlier that the building was "well alight" but it appears that firefighters now have it under control as they added at 11am: "We're starting to scale back our attendance at the fire."
Motorists are warned to expect some disruption on the roads around the site.