FIRE crews are expected to remain at the scene of a major blaze in Darlington for the next 48 hours.
An investigation into the cause of the fire, on the Albert Hill Industrial Estate, is due to get under way.
The alarm was raised at about 7pm on Saturday, when a warehouse containing 5,000 tonnes of general waste caught fire.
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At its height, the incident was attended by 45 firefighters, with other emergency services on standby.
Smoke from the fire could be seen from as far away as Consett.
Group Manager Dominic Brown, of County Durham and Darlington Fire and Rescue service said crews will remain at the scene for much of today and Bank Holiday Monday, although the fire is now well under control.
The cause of the fire is unknown at this stage, but Mr Brown said a joint investigation with the police would follow in due course.
Smoke is this morning blowing in an easterly direction with residents in the Haughton and Middleton St George areas of Darlington are warned the smoke is blowing in their direction.
Mr Brown said advised people in those areas to stay indoors as a precaution.
He added that there is no reason to suspect the smoke contains toxic materials.
Mr Brown said: "Where the smoke is coming across, we are just asking people to avoid it by staying indoors and closing their windows.
"We are happy, having taken advice from the Environment Agency and our own hazardous material managers, that there is nothing particularly toxic about that smoke, it is just general smoke from fire.
"But even that could contain certain chemicals, so we would ask people to avoid if possible, but we are not particularly concerned at the moment."
Mr Brown said crews had been hampered in reaching the fire, as one side of the site is is next to a steep bank leading down to the River Skerne.
He said: "It is under control now, there is no fear of it spreading outside the building, which was our first priority, to prevent that.
"We are identifying hot spots as we go along, there are still flames at the back, but as the fire progresses through the waste, when it reaches an area that is particularly flammable, it will flare up slightly, then we can tackle that."
Eight fire appliances were tackling the blaze at its height, with crews dispatched from as far north as High Handenhold.
Mr Brown added: "Although we have had eight appliances here from across the county, we have always had cover for other areas as well."
He said contact had been made with the site's owners, as well as those from neighbouring properties.