The blast occurred at 11:46am local time on Monday 9 November, triggering a fire and sending thick smoke above the industrial complex. Aerial footage showed emergency vehicles surrounding the site as ambulances transported casualties to nearby hospitals.
İzmir governor Süleyman Elban said an overhead crane had collapsed into an electric arc furnace during maintenance work, damaging a gas line and causing the explosion.
One worker told AFP that a snapped crane cable had sent around 120 tonnes of molten steel crashing onto the furnace, triggering a violent reaction.
Around 200 employees were in the affected area at the time, fewer than usual because production had been suspended for maintenance.
Five people have been detained and four prosecutors assigned to investigate the circumstances of the disaster, while rescue teams continue searching the wreckage.