The search for survivors continued Saturday after a rainstorm sent water spilling out of the Guadalupe River in Texas, sweeping away a girls' summer camp, killing at least 27 people, including nine children, and leaving another two dozen missing. 

The destructive fast-moving river waters rose eight metres in just 45 minutes before dawn Friday, washing away homes and vehicles. More heavy rains were expected Saturday, and flash flood warnings and watches remained in effect for parts of central Texas.

Some 27 people were missing from Camp Mystic, city manager Dalton Rice said at a news conference.

"People need to know today will be a hard day," said Kerrville Mayor Joe Herring Jr. "Please pray for our community."

Searchers used helicopters, boats and drones to look for victims and rescue stranded people in trees and from camps isolated by washed-out roads. The total number of missing people was not known, according to Rice, who said he didn't want to give an estimate.

On social media, parents and families posted desperate pleas for information about loved ones caught in the flood zone.

"The camp was completely destroyed," said Elinor Lester, 13, one of hundreds of campers at Camp Mystic. "A helicopter landed and started taking people away. It was really scary."

She said a raging storm woke up her cabin around 1:30 a.m. local time Friday. Rescuers tied a rope for the girls to hold as the children in her cabin walked across a bridge with floodwaters whipping around the calves and knees. 

Some 850 rescued so far

Kerr County Sheriff Larry Leitha said 27 people, including nine children, were confirmed dead. Authorities said about 850 people had been rescued.

The flooding in the middle of the night on the Fourth of July holiday caught many residents, campers and officials by surprise. The Texas Hill Country, northwest of San Antonio, is a popular destination for camping and swimming, especially around the summer holiday. 

AccuWeather said the private forecasting company and the National Weather Service sent warnings about potential flash flooding hours before the devastation. 

"These warnings should have provided officials with ample time to evacuate camps such as Camp Mystic and get people to safety," AccuWeather said in a statement, adding the Texas Hill County is one of the most flash-flood-prone areas of the U.S. because of its terrain and many water crossings.

Officials defended their actions Friday, saying they had not expected such an intense downpour that was the equivalent to months' worth of rain for the area.

A river gauge at Hunt recorded 6.7 metres in about two hours, according to Bob Fogarty, meteorologist with the National Weather Service's Austin/San Antonio office. The gauge failed after recording a level of 9 metres.

"The water's moving so fast, you're not going to recognize how bad it is until it's on top of you," Fogarty said.

Helicopters, drones used in search for missing

On the Facebook page of the Kerr County sheriff's office, people posted pictures of loved ones and begged for help finding them.

More than 1,000 rescuers were on the ground. Helicopters and drones were in use, and some people were being plucked from trees. U.S. coast guard helicopters were flying in to assist.

In Ingram, Erin Burgess woke to thunder and rain at 3:30 a.m. Just 20 minutes later, water was pouring into her home directly across from the river, she said. She described an agonizing hour clinging to a tree and waiting for the water to recede enough so they could walk up the hill to a neighbour's home.

"My son and I floated to a tree where we hung onto it, and my boyfriend and my dog floated away. He was lost for a while, but we found them."

Of her 19-year-old son, Burgess said: "Thankfully he's over 6 feet tall. That's the only thing that saved me, was hanging on to him."

Search crews were facing harsh conditions while scouring the waterlogged rivers, culverts and rocks. "They are looking in every possible location," Rice said.

One reunification centre at an elementary school was mostly quiet Saturday after taking in hundreds of evacuees the day before.

"We still have people coming here looking for their loved ones. We've had a little success, but not much," said Bobby Templeton, superintendent of Ingram Independent School District.

President Donald Trump said Saturday that Homeland Security Secretary Kristi Noem was traveling to Texas and his administration was working with officials on the ground.

"Melania and I are praying for all of the families impacted by this horrible tragedy," Trump said, referring to his wife, in a statement on his social media network. 

'I was scared to death'

At a reunification centre set up in Ingram, families cried and cheered as loved ones got off vehicles loaded with evacuees. Two soldiers carried an older woman who could not get down a ladder. Behind her, a woman in a soiled T-shirt and shorts clutched a small white dog. 

Later, a girl in a white "Camp Mystic" T-shirt and white socks stood in a puddle, sobbing in her mother's arms.

Barry Adelman, 54, said water pushed everyone in his three-storey house into the attic, including his 94-year-old grandmother and nine-year-old grandson. The water started coming through the attic floor before finally receding. 

"I was horrified," he said. "I was having to look at my grandson in the face and tell him everything was going to be OK, but inside I was scared to death." 

The forecast had called for rain, with a flood watch upgraded to a warning overnight for at least 30,000 people. But totals in some places exceeded expectations, Fogarty said. 

Patrick noted the potential for heavy rain and flooding covered a large area.

"Everything was done to give them a heads-up that you could have heavy rain, and we're not exactly sure where it's going to land," Patrick said. "Obviously as it got dark last night, we got into the wee morning of the hours — that's when the storm started to zero in."

Asked about how people were notified in Kerr County so that they could get to safety, Judge Rob Kelly, the county's chief elected official, said: "We do not have a warning system." 

When reporters pushed on why more precautions weren't taken, Kelly said: "Rest assured, no one knew this kind of flood was coming." 

Popular tourism area prone to flooding

The area is known as "flash flood alley" because of the hills' thin layer of soil, said Austin Dickson, CEO of the Community Foundation of the Texas Hill Country, which was collecting donations to help non-profits responding to the disaster.

"When it rains, water doesn't soak into the soil," Dickson said. "It rushes down the hill."

River tourism industry is a key part of the Hill Country economy. Well-known, century-old summer camps bring in kids from all over the country, Dickson said.

"It's generally a very tranquil river with really beautiful clear blue water that people have been attracted to for generations."