Smoke from the blaze on an industrial estate in Ranskill, south of Bawtry, has been spotted from as far away as Moorends, the Isle of Axholme and across wide parts of South Yorkshire.
Crews are being assisted by Derbyshire, South Yorkshire and Lincolnshire Fire and Rescue Services.
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Two people who were staying on site are being treated by East Midlands Ambulance Service for smoke inhalation.
A spokesman said: “There have been reports of a number of people gathering at the scene, please stay aware from the area and allow our crews to resolve this incident safely.”
More than 1,000 tyres are ablaze after fire broke out this morning shortly before 10.30am.