A dozen fire engines have been sent to deal with the blaze at Catstones Moor, Keighley Road, Cullingworth, Bingley.
Crews were called out just after 3pm today (Sun July 8).
A West Yorkshire Fire Service spokesman, said: "Appliances from across the area are in attendance, with over 50 firefighters dealing with the incident under extreme heat conditions.
"The Fire service is being assisted by NPAS police helicopter in identifying hotspots on the moor.
"Keighley Road and Ryecroft Road are currently closed to traffic and nearby residents are advised to keep their doors and windows closed."
Video: West Yorkshire Fire & Rescue Service.