Fire Service crews was dispatched to Gillen Fuels on the Heather Road at just before 6 pm on Saturday.
William Johnston, the Fire Service group commander, said that the incident is still ongoing.
At the height of the blaze there were 60 fire personnel involved.
Anyone living in the vicinity of the plant was asked to keep their windows and doors closed.
Mr Johnston said it was difficult to get access to the building so they had to do a lot fire fighting from outside the premises.
“It was quite a challenging situation with hundreds of tons of mixed waste involved in the fire.
“We have scaled back the crew at the site but will remain there for the rest of the day,” he said.
“The initial crews attending the fire were from across Northern Ireland.”