Police say there's still a risk a huge dam at Toddbrook Reservoir in Whaley Bridge will fail.
In an update on Friday after an RAF Chinook helicopter dropped more than 50 tonnes of aggregate onto the dam's wall to shore it up, officers urged the public to heed the advice of the emergency services.
Toddbrook Reservoir - which contains 1.3 million tonnes of water - has seen 'extensive' damage during recent flooding and images appear to show a huge, crumbling hole in the dam wall.
More than 1,000 residents have so far been evacuated from Whaley Bridge and surrounding villages.
Police said work to shore up the dam would continue throughout the day.
The Chinook will also be dropping bags of aggregate - a mixture of sand, gravel and stone - into other parts of the reservoir, in a bid to stem the flow of water pouring into it.
Derbyshire Police said late on Thursday that 400 tonnes of aggregate would be brought in by the RAF as part of a multi-agency taskforce.
The Environment Agency issued a 'danger to life' warning covering the River Goyt area and the valley below the dam as the river could 'rise rapidly' due to water rushing in from the reservoir and the potential dam burst.
A small number of properties in the areas of Furness Vale and New Mills, outside Whaley Bridge but inside the flood risk area, were also evacuated on Thursday evening.
Police said in an update: "Throughout the day, work will continue to further shore up the reservoir wall.
"The Chinook will also be dropping aggregate into other parts of the reservoir today, to stem the flow of water going into it.
"There are also a total of 16 high volume water pumps which have been installed in the reservoir, in order to reduce the water levels. These have been provided by fire services from across the country and the Canal and River Trust.
Assistant Chief Constable of Derbyshire Constabulary, Kem Mehmet, said: "Our message today remains the same - as there is still a risk the dam will fail.
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"Please stay away from the area.
"If you are asked to leave, please heed emergency services and expert advice and do so.
"We understand that being asked to leave your home is an extremely difficult and worrying situation to find yourself in, however it is not a decision we have taken lightly and ultimately the safety of the public is our main concern."
The evacuation point at Chapel High School, Chapel-en-le-Frith, would remain open today, police said.
ACC Mehmet said: "We have evacuated more than 1,000 people from the areas that would be immediately affected by floodwater should the wall fail.
"The majority have been able to find accommodation with family and friends.
"About 40 people have also been put up in a local hotel and they will be looked after today.
"We don’t know how long this operation will take to conclude but we and our colleagues in the emergency services, partner agencies, Environment Agency and military are doing everything humanly possible to save the reservoir wall and to protect the town."
The Canal and River Trust, which operates the reservoir, said water levels have gone down by about eight inches overnight.
