A major search and rescue operation is continuing through the night in Texas after flash floods killed at least 24 people and left many girls missing from a Christian summer camp.

There was little warning as the Guadalupe River rose 26 feet (7.9m) in less than an hour and flooding that followed swept away mobile homes, vehicles and holiday cabins where people were spending the 4 July weekend.

Rescue crews are still searching for up to 25 children who were among the 750 girls attending the Camp Mystic just outside the town of Kerrville 104km (64.0 miles) north-west of San Antonio.

A state of emergency has been declared in several counties where several roads have been washed away and phone lines are down.

US President Donald Trump called the tragedy "shocking" and "terrible" as the White House pledged additional assistance.

Pictures show the deep flood waters swamping bridges and fast moving water swirling down roads.

Texas Lieutenant Governor Dan Patrick said: "Within 45 minutes, the Guadalupe River rose 26 feet and it was a destructive flood, taking property and sadly lives."

He also informed parents that if they have not been contacted, their child is accounted for.

"That does not mean [the missing children] have been lost. They could be out of communication," Patrick added.

Officials said search and rescue operations, involving helicopters, drones and boats, will continue until everyone has been accounted for.

The camp said they have no power, no water and no Wi-Fi , adding that "the highway has washed away, so we are struggling to get more help."

On Friday morning, flash flooding in the state prompted disaster declarations for the Hill Country and Concho Valley regions.

Kerr County's most senior official, Judge Rob Kelly, was asked during a news conference as to why camps along the Guadalupe River were not evacuated in advance.

"We didn't know this flood was coming. Rest assured, no one knew this kind of flood was coming," Kelly said.

He then added "we do not have a warning system" in the area. Kelly added what happened on Friday far surpassed a flood in 1987, which killed 10 teenagers on a church camp bus near the town of Comfort, south of Kerr County.

According to the BBC's US partner CBS News, the Texas Division of Emergency Management had multiple meetings on Thursday to prepare, but officials said the National Weather Service "did not predict the amount of rain that we saw".

Original estimates were of up to 8 inches (20cm) of rain.

Officials said they were still concerned about the weather, adding that "if you do not live in area, do not come."

Kerr County Sheriff's Office told residents near creeks, streams and the Guadalupe River to move to higher ground.

Meanwhile, Republican Texas Senator Ted Cruz said President Trump had "committed anything Texas needs".