The road between Waterloo Street and Oxford Street has been closed while firefighters tackle a blaze at a flat above Mayyah Indian takeaway in Queen Street.
Three crews from Market Rasen, Caistor and North Lincoln are at the scene after getting a call at 12.48pm.
Resident Margaret Lakin-Whitworth, who works at the Market Rasen Lincolnshire and Nottinghamshire Air Ambulance shop, said: “There was lots of black smoke coming out of the building.
“No-one can get down to my shop.”
Lincolnshire Fire and Rescue has confirmed there have not been any injuries.
Updates to come