Up to 60 firefighters were called in to tackle a massive blaze at a scrapyard and recycling plant at Campsie on the outskirts of Londonderry.
Police placed a 200-metre exclusion zone around the area after a number of loud explosions were heard.
A total of five fire appliances and four specialist units, including an aerial hose, attended the scene and remained for hours.
The fire service said large amounts of diesel, plastic and cardboard were in the buildings, which caught fire, as well as several gas cylinders.
Staff member Anne Doherty was across the road from the Peak Environmental plant when she noticed the billowing black clouds of smoke.
Speaking to the Belfast Telegraph, she said: “It was the smoke that first caught my attention, but then I noticed the flames rising into the sky.
“We heard a really big bang, like an explosion, shortly after we noticed the fire and you could almost feel the vibration from that,” she added.
The emergency services were still dealing with the aftermath of the fire late last night.