More than 50 homes have been evacuated in Carrbrook, near Stalybridge, Greater Manchester, and 150 people affected.
The fire began on Sunday night, reignited on Monday during the hot weather and then spread throughout Tuesday, fanned by evening winds.
Greater Manchester Mayor Andy Burnham said a "request to the military for extra support" is being prepared "so there is a back-up plan" to support firefighters.
Greater Manchester Police's Saddleworth division said about 2,000 acres of moorland had been destroyed in the fire.
Some 65,000 gallons of water were dropped on the blaze by a helicopter on Tuesday to fight the fire which was "unprecedented in recent times", it added.
