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At least nine people from one family have been killed in flash floods after monsoon-like rains swept through a swimming hole in the US state of Arizona, local media say.

At least 40 rescuers are searching for a 27-year-old man whose wife perished.

More than 100 people were bathing in the area when the muddy floodwaters hit with almost no warning.

The flash flood struck at Cold Springs, near Payson, on Saturday, sweeping people down East Verde River.

Search and rescue crews have recovered the bodies of nine victims, some of whom were found up to two miles down the river.

Four others - a married couple and their two young children - were rescued by helicopter crews and treated for hypothermia.

Dozens were bathing in the Tonto National Forest, about 90m (145km) north of Phoenix, when the floodwaters hit following a torrential downpour upstream, said Sgt David Hornung from the Gila County sheriff's office.

"A large family group was down by the river recreating... It's a recreation area that a lot of people come up to - and the flash flood came through and washed 14 people away from the camp," Sgt Hornung said.

"I've been with the sheriff's office for 13 years and this is the most severe flooding incident we've ever seen," he added.

Video footage posted on social media showed muddy floodwater gushing over rocks and through deep canyons.

The Payson Fire Department said that multiple forest fires in recent months had created piles of debris that burst down a creek, carrying ash-filled water through the swimming hole.

However, it had not been raining in the area where people were swimming.

Officials identified the dead on Monday.

They named one of the victims as Maria Raya, 27, who died a day before her birthday along with her children - Emily, three, Mia, five, and Danial, seven.

Her sister Maribel Raya, 24, and brother Javier Raya, 19, perished, they said, as well as Maribel's daughter Erica, two.

Selia Garcia, 57, the mother of Maria, Maribel and Javier, also died, as did her grandson Jonathan Leon, 13.

All nine were from Phoenix, Arizona.

Maria's husband Hector Miguel Garnica is yet to be located, and is feared to have died alongside his family.

His sister Carla Garnica, 22, was quoted as saying: "He has to be found. He's always said, 'I'm never leaving my children or my wife.' He has to complete his promise."

The Gila County Sheriff's Office said relatives of the missing family drove to the area to search for them into the early hours of Sunday.

Maria Mandujano, a cousin of the Raya siblings, said the searchers waded through knee-deep water shouting her loved ones' names.

They found one of the children's bodies amid the debris, she said.

The National Weather Service has issued a flash flood alert for much of Arizona until Monday evening, with more storms expected in the middle of next week.