Six fire engines remained on scene overnight as a "rapidly developing, aggressive fire" ravaged moorland.
Two large-scale moorland fires merged on Saturday due to increasing wind speed and a major incident was declared as crews tackled the blaze.
Greater Manchester Police said fires on Winter Hill and Scout Road near Bolton have merged, with pedestrians and motorists urged to stay away from the scene.
Lancashire Fire and Rescue Service said the number of crews was reduced overnight and full firefighting operations would begin again at 4.30am.
Greater Manchester Fire and Rescue Service said on Saturday it had 28 fire engines tackling the moorland fires. There were approximately 120 personnel on the moors, split between seven areas of wildfire in Tameside and Winter Hill, Bolton.
Assistant chief fire officer Dave Keelan said: "This is an exceptionally challenging time and I am proud of the hard work and brave commitment of our firefighters."
Lancashire fire service area manager Tony Cook said "very intensive firefighting" is taking place on Winter Hill, including personnel doing shuttle runs in appliances to get water to the scene while others manually try to beat the fire out.
Fire break trenches are also being dug to try to protect local buildings.