Fire crews are battling a blaze on Starbeck High Street.
North Yorkshire Fire and Rescue Service have tweeted to confirm that the former McColl's building is "well alight."
The tweet reads: "We currently have crews from Harrogate, Knaresborough, Boroughbridge and @WYFRS Wetherby in attendance at a derelict building well alight on the High Street, Harrogate. Please avoid the area if you can due to a large amount of traffic congestion leading out of Harrogate."
Eyewitness Meghan Walsh, 12 said fire crews have asked residents to stand 10ft back, and all she could see was smoke. She said Forest Lane has been at a complete standstill.
Nine fire engines have been on the scene.
The landlord of the Prince of Wales pub is giving out free juice and water to emergency services personnel, and schoolchildren have been giving out bottles of water to firemen.
Pictures and video: Meghan Walsh.