Lancashire Fire & Rescue Service are currently attending a scene in Church Street, Preston.
Witness reports indicate there were first around six fire engines at the scene where Church Street meets Birley Street, with several more arriving afterwards.
Fire crews have been spotted preparing hose-reel jets for use.
The appliances arrived at the scene at approximately 1.40pm.
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A statement from Lancashire Fire & Rescue Service said: “999 call reporting smoke from a vent of flat on sixth floor of 12 story building on Birley Street, Preston.
“Two fire engines and crews from Preston, one from Penwortham, one from Bamber Bridge, one from Fulwood and an aerial ladder platform and crew from Preston. Firefighters are on sixth floor investigating source.
“Response of those resources a precaution.”
A section of Church Street has been closed while emergency services deal with the incident.