Several local residents posted images of smoke billowing from the area, with one saying "not again - fire on #Ilkley Moor close to Hangingston Road after the Cattle grid".
West Yorkshire Fire and Rescue Service confirmed that 10 fire engines have been sent out.
They tweeted: "We are aware of a large moorland fire on Ilkley Moor and have crews in attendance and more on the way."
West Yorkshire Police posted: "Hangingstone Road is currently closed while emergency services deal with fires on the moor."
West Yorkshire Fire and Rescue Service said 10 fire engines were attending the Ilkley Moor blaze.
It said it had received more than 65 emergency calls about the fire and said there was "a lot of smoke in the area".
"The public is advised to avoid the area to allow firefighters to tackle the fire," it added.
UPDATE: The fire is largely out as of 11.45am, but crews remain on scene damping down.