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 on Sunday about whether enough warnings were issued in area long vulnerable to flooding and whether enough preparations were made.

The destructive, fast-moving waters rose eight metres on the river in only 45 minutes before daybreak 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.

A day of prayers in Texas

Governor Greg 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. History’s first American pope spoke in English at the end of his Sunday noon (8pm AEST) blessing.

“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.

The hills along the Guadalupe River are dotted with century-old 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.

Harrowing escapes from floodwaters

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 wouldn’t reach them.

At Camp Mystic, a cabin full of girls held onto 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.

Warnings came before disaster

The National Weather Service on Thursday 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.

At the Mo-Ranch Camp in the community of Hunt, officials had been monitoring the weather and opted to move several hundred campers and attendees at a church youth conference to higher ground.

At nearby Camps Rio Vista and Sierra Vista, organisers also had mentioned on social media that they were watching the weather the day before ending their second summer session Thursday.

Authorities and elected officials have said they did not expect such an intense downpour, the equivalent of months’ worth of rain for the area.

US Representative Chip Roy, whose district includes the ravaged area, acknowledged that there would be second-guessing and finger-pointing as people look for someone to blame.