At least 50 people, including 15 children, have been confirmed dead following flash floods in central Texas, authorities said, as rescuers continued a frantic search for campers, vacationers and residents who were still missing.
The hunt for survivors of Friday's river surge included locating dozens of young girls missing from a Christian summer camp.
The sheriff's office in Kerr County said 800 people had been evacuated from the region as flood waters receded in the area around the Guadalupe River, north-west of San Antonio.
"We have recovered 43 deceased individuals in Kerr County. Among these who are deceased, we have 28 adults and 15 children," said Larry Leitha, the sheriff of the flood-ravaged region.
Multiple victims were also found in other counties, bringing the death toll to 50.
It was probable the casualty toll was higher, authorities said, as other counties in the area were afflicted by the flooding.
Among the missing were 27 girls from the Camp Mystic summer camp, Kerrville city manager Dalton Rice said at a press conference on Saturday evening, and there may be others beyond that.
The river waters rapidly rose 8.8 metres near the camp.
Texas Governor Greg Abbott said late on Friday that nearly 18 hours after the crisis began, search-and-rescue operations would press on through the night into Saturday.
Mr Abbott said resources devoted to the effort would be "limitless".
US President Donald Trump told reporters on board Air Force One that "we'll take care of them", when asked about federal aid for the disaster.
"Melania and I are praying for all of the families impacted by this horrible tragedy," he wrote on social media.
The US National Weather Service declared a flash flood emergency for parts of Kerr County in south-central Texas Hill Country, about 100km north-west of San Antonio, after thunderstorms that dumped as much as 30cm of rain.
Dalton Rice, city manager for Kerrville, the county seat, told reporters the extreme flooding struck before dawn with little or no warning, precluding authorities from issuing advance evacuation orders as the Guadalupe swiftly rose above major flood stage.
"This happened very quickly, over a very short period of time that could not be predicted, even with radar," Mr Rice said. "This happened within less than a two-hour span."
State emergency management officials had warned as early as Thursday that west and central Texas faced heavy rains and flash flood threats "over the next couple of days", quoting National Weather Service forecasts ahead of the Fourth of July holiday weekend.
But the weather forecasts "did not predict the amount of rain that we saw", Nim Kidd, director of the Texas Division of Emergency Management, told a news conference on Friday night.
Independence Day firework displays were cancelled in flood-stricken communities throughout the region, including Kerrville, where the waterfront site for a planned Fourth of July celebration was submerged by the rain-swollen river.
At Friday night's briefing, Kerr County Sheriff Larry Leitha said 24 flood-related fatalities had been confirmed, up from 13 earlier in the day.
One more person found dead in neighbouring Kendall County was not confirmed to be a flood-related casualty, he said.
Search for missing girls
Officials said they were searching for 27 girls listed as missing from among more than 750 children at summer camp sites along the banks of the Guadalupe River, Lt Gov Dan Patrick said.
The missing campers had all been attending Camp Mystic, a private Christian summer camp for girls.
"We're praying for all those missing to be found alive," Mr Patrick said.
It was not clear whether anyone unaccounted for might have ended up among the deceased victims tallied countywide by the sheriff.
Otherwise, all other campers were safe, authorities said, and were being evacuated throughout the day.
"Everybody is doing everything in their power to get these kids out," Kerr County Judge Rob Kelly, the top local elected official, had said at a news briefing on the disaster hours earlier.
Mr Kelly said a number of scattered residential subdivisions, recreational vehicle parks and camping grounds were hit hard.
Asked why more precautions were not taken with stormy weather in the forecast, Mr Kelly insisted a disaster of such magnitude was unforeseen.
"We have floods all the time. This is the most dangerous river valley in the United States," he said. "We had no reason to believe this was going to be anything like what's happened here. None whatsoever."
Mr Patrick said the Guadalupe River had risen by eight metres in 45 minutes as heavy showers soaked the region.
As of Friday night, emergency personnel had rescued or evacuated 237 people, including 167 by helicopter.
With additional rain forecast in the region, Mr Patrick warned that the threat of flash flooding extended from San Antonio to Waco for 24 to 48 hours.
On Friday night, Mr Abbott signed a disaster declaration to hasten emergency assistance to Kerr and a cluster of additional counties hardest hit by the floods.
Personnel from the US Coast Guard and the Federal Emergency Management Agency were activated to assist local authorities, officials said.
