Rescue teams are grappling with more rain as the search continues for dozens of people still missing after flash floods hit central Texas, killing at least 78 people.
US search teams waded through mud-laden riverbanks and flew over the flood-stricken landscape on the fourth day of the search for survivors after Friday's flash floods.
The bulk of the dead were in the riverfront Hill Country, Texas town of Kerrville, where 68 were killed including the 28 children, Kerr County Sheriff Larry Leitha said.
The Guadalupe River that runs through Kerrville was transformed by pre-dawn torrential downpours into a raging torrent in less than an hour on Friday.
The dead there included 27 campers and counsellors at the Camp Mystic summer camp, a nearly century-old Christian girls' retreat on the banks of the Guadalupe River, the camp said in a statement.
As of late Sunday afternoon, state officials said 10 other flood-related fatalities had been confirmed across four neighbouring south-central Texas counties, and that 41 other people were still listed as unaccounted for beyond Kerr County.
Freeman Martin, director of the Texas Department of Public Safety, predicted the death toll would rise further as flood waters receded and the search gained momentum.
Authorities also warned that continued rainfall, even if lighter than Friday's deluge, could unleash additional flash floods because the landscape was so saturated.
The National Weather Service said that heavy rains and thunderstorms could cause more flooding across the area on Monday.
State emergency management officials had warned on Thursday, ahead of the July Fourth holiday, that parts of central Texas faced the possibility of heavy showers and flash floods.
But twice as much rain as was predicted ended up falling over two branches of the Guadalupe just upstream of the fork where they converge, sending all of that water racing into the single river channel where it slices through Kerrville, City Manager Dalton Rice said.
Search and rescue operations are continuing around the clock, with hundreds of emergency personnel on the ground contending with a myriad of challenges.
"It's hot, there's mud, they're moving debris, there's snakes," Martin told reporters on Sunday.
Officials said on Saturday that more than 850 people had been rescued, some clinging to trees, after a sudden storm dumped up to 38 centimetres of rain across the region, about 140 km northwest of San Antonio.
The Federal Emergency Management Agency was activated on Sunday and was deploying resources to Texas after President Donald Trump issued a major disaster declaration, the Department of Homeland Security said.
US Coast Guard helicopters and planes were aiding search and rescue efforts.
Trump said on Sunday he would visit the disaster scene, probably this Friday.
He has previously outlined plans to scale back the federal government's role in responding to natural disasters, leaving states to shoulder more of the burden themselves.
Some experts questioned whether cuts to the federal workforce by the Trump administration, including to the agency that oversees the National Weather Service, led to a failure by officials to accurately predict the severity of the floods and issue appropriate warnings ahead of the storm.
Trump's administration has overseen thousands of job cuts from the National Weather Service's parent agency, the National Oceanic and Atmospheric Administration, leaving many weather offices understaffed, former NOAA director Rick Spinrad said.