Mid and West Wales Fire and Rescue Service said several crews have been sent to tackle the developing blaze at on Pontardulais Road in Gorseinon, Swansea.
Residents and businesses affected by smoke have been advised to stay indoors, close windows and doors, and turn off any air conditioning or ventilation units.
Anyone travelling through the area was told to take precautions.
A statement from Mid and West Wales Fire & Rescue Service said:
“At 3.04pm on Friday, September 20th, Mid and West Wales Fire and Rescue Service crews from Gorseinon, Pontarddulais, Morriston, Swansea Central, Port Talbot and Pontardawe Fire Stations were called to an incident at the old Gorseinon School on Pontardulais Road.
“This incident is currently ongoing and crews are responding to a derelict building that is well alight and fully involved in fire. Crews are utilising hose reel jets and breathing apparatus to fight the fire.
“More information will be released when available.”
