Firefighters could be at the scene of a County Durham fire for days, residents have been warned.
Crews from across the county were called out to the former Eldon Brickworks site near Bishop Auckland early on Monday morning.
Residents were warned to close their windows as the unknown materials burning could be potentially hazardous.
A huge plume of smoke filled the sky and could be seen from miles away, with smoke reaching the A1.
Due to the volume and unknown nature of the waste, firefighters are using a controlled burn to tackle the fire in a bid to reduce the pollution from the fire.
Group incident commander Graeme Metcalf warned residents firefighters would be on the scene for a number of days.
He said: “It was a large fire that was identified on arrival. Currently we have six appliances in attendance, a number of specialist appliances and an aerial ladder platform so we can pump water from above due to the state of the building that is in danger of collapse.
“There is around 500 tonnes of baled and unseparated waste inside the building.
“We are working with our colleagues and the Environmental Agency, and one of our concerns is the pollution as a result of our fire fighting activity because the waste is essentially unidentified at this point in time.
“We are using a controlled burn for this incident so what we are doing is limiting the amount of water we are putting on to limit the pollution that goes up in the plume."
Crews are also working with the operators on site to pull the waste apart into smaller batches so it will burn out quicker.
Mr Metcalf added: “We are using limited water to try and protect the surrounding area. I think due to the approach we are taking unfortunately there will be some impact over the next three to four days at the very least, potentially up to five or six days.
“We are essentially going to operate mainly in the day time and still have crews here in the evening - a 24 hour presence for around three or four days - but we will scale down operations in the hours of darkness for safety reasons.”
Mr Metcalf said the cause of the fire was still unknown but an investigation would take place in due course.
Members of the public in the Bishop Auckland, Eldon, Eldon Lane, Coronation and South Church areas were advised to keep their doors and windows closed due to large amounts of smoke and possible hazardous materials being involved.
Claire Jefferson, 52, who lives next door to the site, said: "My husband got up at 5am because he saw the blue lights.
"A police car was outside and fire engines started coming at the early hours. There were flames coming out the top and a plume of smoke.
"You don't know what's in it, it could have been gas bottled or anything.
"There have been at least eight engines in and out all morning."
