A blaze on Marsden Moor could get worse as the day becomes hotter, firefighters have warned.
The fire - believed to have been started by a barbecue - broke out last night.
As it stands, there are 15 crews on scene attempting to fight the flames, with West Yorkshire Fire and Rescue Service also drafting in water air support.
Astonishing footage shared by Slaithwaite Fire Station shows a helicopter dropping water onto the fire from above.
It's understood the buckets carried by the helicopters can carry thousands of gallons of water.
A HVP - high volume pump - is also being brought in so that crews can take water from local reservoirs to help try to extinguish the blaze.
Smoke from the fire can be seen for miles around, including as far as Rochdale, Oldham, and Tameside.
Several roads - including in the A640 in Denshaw near Dowry Reservoir and Saddleworth Road in Deanhead, West Yorkshire, near Ringstone Edge Reservoir - are currently closed in both directions as a result of the blaze.
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Dave Teggert, group manager with West Yorkshire Fire and Rescue, said crews were first called to the moor just before 6.30pm on Sunday.
He said 10 crews were originally scrambled to the scene, but that this was reduced through the night as firefighters struggled to access the moorland in the dark.
"There are currently 15 pumps in attendance," he added.
"There is also water air support, and a HVP is being brought in to bring water from local reservoirs - high volume pumps allow us to transport water large distances."
Dave said the fire has engulfed around 100 hectares of moorland, which is the equivalent of around one square kilometre.
He predicts that as the day gets warmer, the fire will get worse.
"As the heat of the day continues to rise we would expect the fire to get potentially worse.
"That's the way wildfires work, they subside through the night because it's cooler, but unfortunately in the day with the heat we do see an increase in flame height.
"It's a case of doing what we can to deal with the fire and as things start to cool down we can look at a 'fire attack' to try and tackle it."
Elsewhere, crews from West Yorkshire are also battling a second moorland fire on Ilkley Moor.
A helicopter is also providing water air support to firefighters there.
In the Peak District - just on the Tameside border - Derbyshire Fire and Rescue Service are dealing with another blaze at Tintwistle, near Glossop.
Crews from Greater Manchester Fire and Rescue Service are assisting.
People living nearby to any of the fires are urged to keep windows and doors closed due to the smoke.
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