More than 50 firefighters battled a large blaze at Tata Steel in Rotherham overnight.
People living close to the plant were warned to keep their windows and doors closed as a precaution due to amount of smoke in the area.
"Several thousands" of litres of oil were ablaze, South Yorkshire Fire and Rescue Service said.
Tata said the fire happened “during a normal steel treatment process” and that an investigation had now been launched.
Site production is back up and running, spokesman added,
Crews were called shortly after 1am on Thursday morning.
At its height, ten fire engines and more than 50 firefighters were tackling the fire, and they were able to contain it to one building by 3am.
A high volume pump was set up to help firefighters access water from an on site reservoir.
By 4am, some of the fire engines were able to leave the scene.
South Yorkshire Fire were able to extinguish the fire and all engines left the scene by 7am.
Residents were also asked to stay away from the site, on Aldwarke Lane, whilst emergency services were at work.
A spokesperson for South Yorkshire Fire said: “All on site personnel have been safely evacuated and there are no reports of any injuries.
“An investigation into the cause of the fire will begin once the fire has been fully extinguished and the scene has been made safe.”
Fire engines from Rotherham, Parkway, Central, Elm Lane, Edlington, Dearne, Birley Moor, Stocksbridge and Tankersley stations were in attendance.
A Tata Steel spokesman said: “There was a fire at the Bright Bar Rotherham facility. There were no injuries and the fire was contained before being extinguished.
“An investigation into the cause of the fire, which happened during a normal steel treatment process, has been launched.”