Firefighters are currently tackling the blaze close just off the A62 Manchester Road near Diggle.
Dramatic pictures from the scene show how a massive wall of flames has turned the night sky orange.
Initial reports are the fire is some 200m x 200m – about the size of one-and-a-half football pitches.
The road between the Colne Valley and Diggle is currently closed in both directions to protect the public, reports Examiner Live .
The closure is in place from Mount Road, near the Carriage House pub to the former Great Western pub.
Two fire crews are reported to be at the scene, which is on National Trust property at Marsden Moor.
We’ll bring you the latest updates in the blog below.
This map shows the location of the fire
‘Never seen anything like this’
People living near by describe the blaze as ‘terrible’.
Video from the scene
Extra crews being drafted in
Our colleagues on the Huddersfield Examiner are also covering this story and they’re reporting more firefighters have been drafted in in the last hour.
The blaze began at 7.30pm with two crews – that’s roughly 10 firefighters – battling the flames.
Local reports are that the manpower has since been doubled.
Details of road closure
Pictures from the scene
These pictures, taken by Nick Lawton, give an indication of the size and scale of the blaze