Firefighters have had to stop work and retreat from battling the wildfires near Bolton after two enormous blazes merged into one.
The week-long battle around Winter Hill, which is a key communications hub for the North West, has now been declared a major incident.
Firefighters had been making progress with the fires on the western side of the hill but throughout Saturday morning high winds pushed another huge fire towards the hill from the east.
The enormous smoke-clouds from the eastern wildfire turned daylight into near-darkness at the summit, with visibility down to just a few yards in places.
Phil Whittaker, from Lancashire Fire and Rescue, was driving through the smoke and told Sky News: "It's quite surreal, it's like being drawn into darkness, into night time."
The Lancashire crews that were still fighting the fire with hoses, beaters and garden leaf blowers – which cool down the air around the flames – had been determined to carry on even though they could see the other fire approaching.
Firefighter Trina Burrow explained: "It is demoralising, you feel like you are fighting a losing battle but you have just got to keep trying."
Resident Phil Farnworth, who was still walking his dog on the hill as the fire crews battled on nearby, described the approaching smoke cloud from the east as "a bit of a monster."
At lunchtime the evacuation messages came over their radios. Fire chiefs in the command unit at the bottom of the hill had decided it was too dangerous to keep them working in the diminishing land between the two fires.
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Extra fire crews, police and other support services have now arrived at Winter Hill to support the operation.
Earlier in the week police confirmed that they had arrested a 22-year-old on suspicion of deliberately starting one of the fires in the area around Bolton.
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