About 100 soldiers and an RAF Chinook helicopter are due to arrive in Greater Manchester to help tackle a vast moorland blaze.
The troops from the 4th Battalion, Royal Regiment of Scotland, were being sent overnight to join firefighters across Tameside, on the edge of Saddleworth Moor.
Related: Saddleworth Moor fire: Wigan firefighters called into action
Some 55 firefighters, including crews from Wigan, were still trying to quell multiple pockets of flames spanning up to 3.7 miles (6km) on Wednesday night.
The soldiers were heading from their barracks in Catterick and will operate out of an Army training centre to control the fire by managing water lines and fire beating, among other means of support.
Defence Secretary Gavin Williamson said it is a display of British troops protecting the UK "no matter the time, no matter the place, and no matter the problem".
The troops were answering a call for assistance from Greater Manchester Fire and Rescue Service (GMFRS).
The Chinook, which will fly out of RAF Odiham, Hampshire, on Thursday morning, will move high-volume pump equipment by air to help douse the flames in difficult to access areas.
Dave Keelan, director of emergency response at GMFRS, had also suggested it could be used to transport firefighters.
He said firefighters were working "extremely hard in really hot conditions" but morale was high, adding: "It's more of a task to get them down here to rest."
Problems faced included frequent changes in wind direction, the peat-embedded terrain which requires large quantities of water to extinguish flames and the searing temperatures.
As of Wednesday lunchtime there were seven separate fire incidents ongoing on areas of the moors, including Calico Crescent, Intake Cottage, Intake Lane, Caste Farm, Dovestones, Higher Swineshaw and Chew Road.
Firefighters used beaters and specialist wildfire equipment to tackle the flames.
In addition, Greater Manchester Police deployed a helicopter to assess the scene and United Utilities provided a helicopter that can be used to drop water on to remote areas.
The blaze had been brought under control having started on Sunday, but it reignited the next day and has continued in one of the worst moorland fires to hit the region.
The impact could even be seen from space as Nasa satellites picked up the plumes of smoke.
Some 34 households were evacuated in Calico Crescent in the village of Carrbrook, Stalybridge, on Tuesday night but residents were allowed to return after air quality assessments.
Air quality levels in the area are being monitored regularly in different locations with people in affected areas urged to follow advice from Public Health England and keep their windows and doors closed.Experts warned that high levels of pollutants generated from the blaze could have a significant effect on people's health.
Hugh Coe, professor of atmospheric composition at the University of Manchester, said plume peak concentrations were "very high" and air quality close to the fire was "very poor".
He said pollution plumes have been detected in the centre of Manchester.
Four local schools decided to close on Wednesday for the safety of their pupils but one - Mossley Hollins High - will be open on Thursday as normal.
"The situation in the building and valley has improved," the school said.
No rain is forecast for Tameside for the rest of the week at least.
The cause of the original seat of the fire - thought to be at Buckton Hill, which is land above Buckton Vale, Carrbrook - has not been established but fire chiefs said a detailed investigation would be launched at the appropriate time.
One possible line of inquiry could focus on the frequent gathering of off-road bikers - many not displaying registered plates - at a nearby large quarry.
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Tony Hunter, of Greater Manchester Fire and Rescue Service, said the military will provide "effective support and additional resources" and an RAF helicopter is also available.
"The moorland is very difficult to access, our 4x4s can do a role but getting heavier equipment is essential for the helicopter," he told reporters.
He added: "It's extremely deceiving at the moment, it looks like it's smouldering away, which it is doing, but with a pick up of the wind we could see pockets being established - we need to keep on top of it.
"We have got square miles of unburnt fuel up there and if there's a change in wind direction or an increase in temperature we could see that go up."
Mr Hunter told reporters: "We can see this being prolonged for days if not weeks, particularly with the fact that the wind has drawn the fires towards the residential but actually away from the centre of the moor.
"We only need a change in wind direction to then see that fire increasing into where the greater fuel source is, so we could see a dramatic change."