More than 30 homes have been evacuated as a large wildfire continues to spread across Saddleworth Moor, with strong winds driving the flames closer to residential areas.
The Army is on standby as dozens of firefighters battle the blaze in Greater Manchester, which is reported to be more than three miles wide. Smoke and flames can be seen for miles.
A major incident has been declared and 34 homes in Carrbrook, in Stalybridge, have already been evacuated. Others were advised to keep their windows and doors closed, while at least two schools are shut on Wednesday due to fears about smoke.
The fire began on Sunday before reigniting on Monday during the heatwave. It spread throughout Tuesday, fanned by winds in the evening. The cause is not yet known, but the blaze has devastated land around Carrbrook.
Crews worked through the night as they sought to get to grips with the fire. Greater Manchester Police said: "We are in contact with the Army and they are on standby to help if we need them."
Images posted on social media showed bright orange flames lighting the night sky, while smoke from the fire can be seen for miles.
No injuries have been reported as a result of the fire, but people living nearby have been advised to keep windows and doors closed by Public Health England.
Greater Manchester Fire and Rescue Service group manager for Tameside, Phil Nelson, said: "Crews are still tackling this difficult fire and are working hard to contain the blaze and prevent further fire spread.
"Firefighters are faced with very difficult circumstances, intense heat and are working on challenging terrain.
"Our main considerations are for crew welfare. It is physically draining working at this incident and it is vital that our firefighters have regular breaks and that relief crews are available to take over."
Speaking about the overnight operation to battle the Saddleworth Moor fire, Leon Parkes, assistant chief fire officer with Greater Manchester Fire and Rescue Service, told reporters: "Fire crews have been working in tremendously difficult conditions in the heat, smoke, working with our partner agencies.
"A number of actions were put in place including the evacuation of nearby houses because of the spread of the fire. We are doing an assessment on the scene this morning. We have 10 fire engines with 50 firefighters.
"Some earth sampling was undertaken last night and the readings that have come back are showing safe levels.
"Our advice to members of the public is to close your windows and doors if you are experiencing smoke. Anybody on medication, continue to take that medication. The feedback in respect of the smoke is that they're at safe levels."
Mr Parkes added: "The evacuation was just over 30 homes last night, there were a number of other homes at threat of fire, however we put additional services in that area so I hope we've quelled that risk.
"The area is really, really large - it's a really difficult fire situation because of the size of it, some of the feedback we've received is that it's over 6km.
"Clearly the challenges are enormous. We have fire fighters working in really, really hot conditions. They're doing everything they can to control that fire.
"As you can appreciate, firefighters will have fire kit on which is heavy, thick, warm - the ground is really hot, the smoke coming off the fire is thick."
He added: "The scenes of fire are not where we can access, some of them are two miles away (from where we can park).
"We've got over 6km of affected area - there is fire occurring in pockets around the outskirts.
"The plan today is to try and really really put some resource on the scene, and put a heavy attack on this fire.
"If that needs military assistance, that's what we'll consider."
Mr Parkes added: "This fire is particularly large. We've got lots of experience with dealing with moor fires.
"But this particular incident is vast - it's presented some real challenges to the fire and rescue service in terms of access, the conditions for firefighters, and obviously the wind encourages the fire to spread.
"We've been dealing with an escalating incident and we are trying to get on top of it now."
He said it had not been established what might have caused the fire.
The huge plumes of smoke stretching along moorland in the north-west of England can be seen in pictures and footage from near the scene.
As dawn broke on Wednesday, police tweeted a picture showing a huge cloud of smoke, saying: "It is going to be a long, hot, smoky day."
People living near the fire told how they could "barely see" when they went outside.
“It’s getting a bit frightening," 28-year-old Dee Blanchard told the Manchester Evening News.
“We’ve got double glazing, but we’ve had to put damp towels around their windows and doors. You can’t go outside, you can barely see.
“The firefighters are trying to connect hoses to hoses because there’s no access point near them."
Meanwhile, the mayor of Greater Manchester Andy Burnham thanked fire crews.
He said: "Huge thanks to the GM firefighters working flat out to contain this worrying situation."