Dramatic pictures show the aftermath of a series of explosions at the Tata steelworks in Port Talbot
Police and emergency services were at the scene after it received "numerous calls" at around 3:30am on Friday morning following a series of blasts.
Locals reported being woken by the sound of an explosion at the steelworks.
One tweeted: "There was just a big explosion from Port Talbot steelworks that just shook the house, hoping no one was hurt."
South Wales Police said it believes the explosion came from a train carrying molten metal on the site. It said two people received minor injuries and they have been released following treatment.
Mid and West Wales Fire and Rescue Service said ten of their appliances were at the scene at the height of the fire. Crews left at 8:40am on Friday morning, handing over responsibility for the incident to Tata.
In a statement, Tata Steel said the incident involved "a spillage of molten iron."
Shortly after 3.30am today there was an incident at our Port Talbot site involving a spillage of molten iron.
The organisation later said that they were "working closely with relevant agencies including the Health and Safety Executive".
A spokesperson added:
"Customer orders have been unaffected and we continue to supply steel to both customers and our downstream businesses by using existing stocks. Meanwhile we are working towards bringing at least one of the two blast furnaces back online within 48 hours".
Video footage from a nearby house on Margam Road appears to show the moment the explosion happened.
Josh Adams told ITV News the "tremor was incredible. It shook the foundations of my house."
This video of the aftermath of the incident was captured by Lance Davies.
Locals describe waking up in the early hours of the morning to "huge bangs and big flares". One woman living nearby said she thought the explosion "was a bomb".
South Wales Police released an update confirming there was "no need for concerns" with regards to potentially "hazardous effects" from the fire.
Eyewitness Damian Healy tweeted a picture of smoke billowing from the site, he said: "The steel works is the heart of this town, our workers Notre Dame".
MP for Aberavon, Stephen Kinnock, has called for a review of the incident.
He tweeted that the explosion "raises real concerns about safety" and added "it could have been a lot worse".
South Wales West Assembly Member, Bethan Sayed, said "safety at the works is of paramount concern".
She added: "Not only must we protest our workforce, but ensure safety and security for residents nearby".