Two people have been treated for smoke inhalation at the scene of a fire involving about 1,000 tyres.
Emergency services were called to an industrial site in Ranskill, Nottinghamshire, at 10:23 BST after thick smoke was seen.
Nine crews, along with the aerial ladder platform, have been deployed to bring the flames under control.
Fire officers said the two casualties were staying on site and have been treated by paramedics.
After reports of groups gathering near the fire, the public were urged to keep away and keep their windows and doors shut.
Nottinghamshire Fire and Rescue Service said it was being assisted by colleagues from Derbyshire.
An investigation into the cause is expected to start as soon as the area is safe.