The death toll from the devastating flooding in Texas has risen again as rescuers continue to search for 11 missing campers and a camp worker.

Dozens of people have been killed since raging floodwaters slammed into central Texas on Friday.

The death toll rose to nearly 70 on Sunday after searchers found more bodies in the hardest-hit Kerr County. The victims include children who were camping along the banks of the Guadalupe River.

Officials have said they will not stop searching until every person is found.

US president Donald Trump declared the deadly flooding in Texas to be a major disaster under the Stafford Act on Sunday.

“I have authorized federal relief and recovery assistance in the affected area,” said a letter signed and posted to social media by Trump to Texas’s governor Greg Abbott.

“Individual Assistance and Public Assistance will be provided.”

Trump has designated the Department of Homeland Security’s Federal Emergency Management Agency (FEMA) to coordinate assistance efforts.

Besides the 59 dead in Kerr County – 38 adults and 21 children – additional deaths were reported in Travis, Burnet and Kendall counties.

Rescuers dealt with broken trees, overturned cars and muck-filled debris in a difficult task to find survivors.

[ Texas floods: The girls camp where 20 children are missing is nearly a century oldOpens in new window ]

Authorities still have not said how many people are missing beyond the children from Camp Mystic, a Christian summer camp where most of the dead were recovered.

With each passing hour, the outlook became more bleak. Volunteers and some families of the missing who drove to the disaster zone began searching the riverbanks despite being asked not to do so.

Authorities faced growing questions about whether enough warnings were issued in an area vulnerable to flooding and whether enough preparations were made.

The destructive, fast-moving waters rose about eight metres on the river in only 45 minutes before daybreak on Friday, washing away homes and vehicles. The danger was not over as flash flood watches remained in effect and more rain fell in central Texas on Sunday.

Searchers used helicopters, boats and drones to look for victims and to rescue people stranded in trees and from camps isolated by washed-out roads. Officials said more than 850 people were rescued in the first 36 hours.

Governor Abbott vowed that authorities will work around the clock and said new areas were being searched as the water receded. He declared Sunday a day of prayer for the state.

“I urge every Texan to join me in prayer this Sunday – for the lives lost, for those still missing, for the recovery of our communities, and for the safety of those on the front lines,” he said in a statement.

In Rome, Pope Leo XIV offered special prayers for those touched by the disaster.

“I would like to express sincere condolences to all the families who have lost loved ones, in particular their daughters who were in summer camp, in the disaster caused by the flooding of the Guadalupe River in Texas in the United States. We pray for them,” he said at the end of his Sunday noon blessing.

The hills along the Guadalupe River are dotted with youth camps and campgrounds where generations of families have come to swim and enjoy the outdoors. The area is especially popular around the Independence Day holiday, making it more difficult to know how many are missing.

“We don’t even want to begin to estimate at this time,” Kerrville City manager Dalton Rice said on Saturday.

[ What we know about the victimsOpens in new window ]

Survivors shared terrifying stories of being swept away and clinging to trees as rampaging floodwaters carried trees and cars past them. Others fled to attics inside their homes, praying the water would not reach them.

At Camp Mystic, a cabin full of girls held on to a rope strung by rescuers as they walked across a bridge with water whipping around their legs.

Among those confirmed dead were an eight-year-old girl from Mountain Brook, Alabama, who was at Camp Mystic, and the director of another camp up the road.

Locals know the area as “flash flood alley”, but the flooding in the middle of the night caught many campers and residents by surprise even though there were warnings.

The US National Weather Service on Thursday had advised of potential flooding and then sent out a series of flash flood warnings in the early hours of Friday before issuing flash flood emergencies – a rare alert notifying of imminent danger. – Associated Press