A major fire involving 15,000 tonnes of tyres at a recycling plant in North Yorkshire will "go on for days", the county's fire chief has said.
Nigel Hutchinson said the cause of the blaze at Newgen Recycling in Sherburn-in-Elmet was not yet known.
About 70 firefighters from across Yorkshire have been at the Lennerton Lane plant since 08:40 GMT.
Residents and school pupils were told to stay indoors as a plume of fumes billowed over nearby villages.
Mr Hutchinson said: "It is a significant fire and one that is difficult to tackle. It's the sort of incident that will go on for days.
"We are anticipating a large part of the stack, if not the whole stack, being involved."
An eyewitness who works at the airfield in Sherburn-in-Elmet told BBC Radio York that he could see flames the height of the hangars at the airfield - at least 20-30ft (7-10m) high.
"It's absolutely colossal. It's like a tornado when you look at it close up, with the heat swirling and all the rest. It's absolutely amazing," he said.
Twelve schools and a children's centre have been advised to keep staff and pupils inside, according to North Yorkshire County Council.
A spokeswoman said: "There will be further advice to schools as the day goes on. More schools and children's centres may be contacted depending on the wind direction."
Environment Agency officers are at the scene to help minimise the impact on the air and water.
Some flights at a nearby airfield have been grounded because of the smoke.
Chris Stringer, chief flight instructor at Sherburn Aero Club, said it has cut off the eastern approach to the airfield.