The blaze, close to Gypsy Lane, Swindon, started just before 01:00 BST and at one point more than 50 firefighters were on site.
People living nearby were earlier urged to keep their windows shut because of thick plumes of smoke caused by the blaze.
Crews are expected to be on site for much of the day.
Station manager Gareth Evans said the fire affected a mound of metal which he described as about 15 sq m big and originally about six metres high.
"That's burnt down now," he said.
"Metal burns with a very, very intense flame so there is the potential for temperatures in excess of 1,000C in that part of the fire."
Mr Evans said the blaze produced "vast quantity of smoke" which could be seen all over the town.
"I don't know what's in that smoke but please close your windows and stay indoors and don't breath the smoke," he added.
A spokesman for European Metal Recycling confirmed the fire started at its Swindon depot early on Saturday.
He said: "While we investigate the cause, we would like to apologise to the local community and businesses for the inconvenience this incident may have caused."
A large fire broke out in a recycling yard, causing plumes of smoke to be seen from miles away.