Hundreds of homes were evacuated in a Derbyshire town on Thursday when a dam threatened to burst after being damaged during extreme rainfall.

Around 1,400 people in 400 houses in Whaley Bridge were told to leave their properties with just minutes’ notice due to “an unprecedented, fast-moving, emergency situation” caused by heavy downpours.

Toddbrook reservoir – which contains around 1.3m tonnes of water – suffered extensive damage during the flooding on Thursday, with images showing a huge hole in the dam wall.

The Environment Agency issued a “danger to life” warning covering the river Goyt, as it could “rise rapidly” owing to water rushing in from the reservoir.

Derbyshire police said 400 tonnes of aggregate would be brought in overnight to divert water from entering the reservoir, with an RAF Chinook helicopter aiding a multi-agency taskforce.

Facebook Twitter Pinterest The partially collapsed dam wall at Whaley Bridge. Photograph: Rod Kirkpatrick/for the Guardian

Deputy chief constable Rachel Swann said: “To move the substantial amount of aggregate into place a Chinook helicopter will be operating in the area in the coming hours to allow precise placement and divert the flow of the water.

“With all that said, at this time the future of the dam wall remains in the balance and I would remind people of the very real danger posed to them should the wall collapse.”

On Thursday night firefighters deployed from across the country were using at least 10 high volume pumps to reduce the water to a safe level before work begins to repair the dam wall.

Many residents left their homes without time to pack a bag, grabbing medicines and pets and heading to a high school in nearby Chapel-en-le-Frith, where a respite centre was set up. Some did not even have a coat; others were bundled out without time to put socks on. They munched on chips and free sandwiches from a nearby Co-op as rain lashed the school windows, watching BBC news in case the dam collapsed.

Some workers rushed home from work after seeing images on the TV only to be refused access to their properties.

Anne Muskett lives on Goyt Road, a cul-de-sac right by the river Goyt, which runs through the middle of Whaley Bridge. Her road ends at the Memorial Park, at the foot of the dam, which has stood above the village for almost 200 years. Police told her she was not allowed back to fetch the neighbour’s cat, Heidi, who she was looking after. “I feel really worried, really upset. The cat treats my home as a second home, I’m like her second mum,” she said. “If the dam goes and the village does flood, she’s stuck in the kitchen.”

Her friend Marella Cairns was in a wool shop in a nearby village when the news came through. She managed to wake her son’s girlfriend and order her to leave, taking with her just the two dogs, Bo and Pip, some medication and her knitting – “all the important things”.

Facebook Twitter Pinterest A police officer blocks the road leading to Toddbrook reservoir. Photograph: Danny Lawson/PA

Like many residents, Cairns blamed global heating – plus overdevelopment of land that used to provide natural flood defences: “Of course this extreme weather is evidence of climate change. We never used to have weather like this. Hopefully now the planners will listen and understand why we don’t want 300 more homes to be built on fields where water can run off from the hills.”

At Chapel high school, Barry Lewis, the leader of Derbyshire county council, said he didn’t know when people would be allowed back home. “We need to get the water levels down in the reservoir first,” he said.

He praised staff for ensuring that all vulnerable residents were evacuated and accounted for. “We think there are around 400 properties immediately affected, which could be around 1,400 people looking for somewhere else to stay tonight. Most people will be staying with families, but we will help those with nowhere to go.”

Flood risk maps showed that if the dam burst it could leave parts of Whaley Bridge and many areas downstream along the river under as much as two metres of water.

Derbyshire police said the decision to evacuate had “not been taken lightly” but described it as “an unprecedented, fast-moving, emergency situation”.

Whaley Bridge is a small town on the edge of the Peak District bisected by the Goyt, which runs down from Buxton and towards Stockport. Popular with outdoor types who commute in to Manchester, it also has a significant population of retirees and older people.

Facebook Twitter Pinterest A view from the top of Toddbrook Reservoir, showing the stormwater erosion. Photograph: @fraglast/PA

Built in 1831, the Toddbrook reservoir sits high above the town, which has a number of pubs, restaurants, a bakery and two chip shops on the main street, as well as a primary school and cricket club.

Among the residents taking sanctuary at Chapel high school was Tony Gunner, who runs the Goyt Inn, just off Whaley Bridge’s main street, with his partner, Jennifer Grant. Gunner was very reluctant to leave the pub after police told him to evacuate. “Ninety per cent of me wanted to stay put. It’s my pub, my beer – my baby. We’ve had the pub for 11 years now and I didn’t want to go.”

Peter Willis, 70, lives in Cromford Court, sheltered accommodation on the outskirts of Whaley deemed at risk of flooding. He had not yet found a place to stay by 7pm on Thursday but was stoical, despite leaving his home with no socks on. “We’re safe, that’s the main thing. We’re in the laps of the gods now,” he said.

The Environment Agency issued a severe flood warning for the area just before 2pm amid concern over damage to an earth dam on the town side of the Toddbrook reservoir, where a concrete spillway is designed to take excess water into the Goyt. On Wednesday evening torrents of water had flowed straight over the barrier “like Niagara Falls”, according to Chris Gay, commodore of the Toddbrook sailing club. The waters subsided slightly on Thursday morning, revealing significant damage to the spillway.

Play Video 1:09 Bridge collapses after flash floods in North Yorkshire – video

Such earth embankment dams are at serious risk of being quickly washed away if the concrete spillways that protect them are damaged, according to Mohammad Heidarzadeh, an assistant professor of civil and environmental engineering at Brunel University London.

“In embankment dams, spillways are extremely important, because they prevent embankment dams from overtopping,” he said. “Due to heavy rainfall ine the Whaley Bridge area, the spillway is now broken and a big chunk of its concrete structure is damaged. There is a possibility that the spillway could then become fully broken in a few hours. If the spillway is fully gone, the embankment dam will be washed away very rapidly, which could cause a massive flood.”

Wednesday’s downpours caused chaos across the north of England. A major incident was declared late on Wednesday evening in Poynton, Cheshire, where thunderstorms and downpours forced drivers to abandon their vehicles and caused damage to property. The wet weather also caused rail disruption on the line between Manchester airport and Wilmslow early on Thursday.

Poynton fire station said its crews had attended more than 20 incidents, rescuing at least 11 people from floodwaters in a four-hour period.

Police in nearby Wilmslow said officers were dealing with flooding and had evacuated homes, with Oakenclough children’s centre open as a rest centre.