About 850 people have been rescued so far.

At a news conference on Saturday afternoon, Texas Governor Greg Abbott said he had signed an expanded disaster declaration to boost search efforts.

He said officials would be relentless in ensuring they locate “every single person who’s been a victim of this event”, adding that “we will stop when the job is completed”.

It remains a search and rescue mission, officials said, not a recovery effort.

They said rescuers were going up and down the Guadalupe River to try to find people who may have been swept away by the floods.

US President Donald Trump said his administration was working closely with local authorities to respond to the emergency.

Forecasters have warned that central Texas may see more flooding this weekend.

The National Weather Service (NWS) said the area could see 2 to 5in (5cm to 12cm) of rain on Saturday.

Up to 10in of rain was possible in some areas badly affected by Friday’s deluge.

Much of the rescue has focused on a large all-girls’ Christian summer camp called Camp Mystic, located along the banks of the Guadalupe River.

Texas Lieutenant Governor Dan Patrick told the BBC’s Radio 4 PM programme many of 27 missing girls were “under the age of 12”.

Pictures from the camp show it in disarray, with blankets, mattresses, teddy bears and other belongings caked in mud.

Many were asleep when the river rose more than 26ft (8m) in less than an hour in the early hours of Friday.

In an email to parents of the roughly 750 campers, Camp Mystic said that if they had not been contacted directly, their child had been accounted for.

Bodies of more children recovered Saturday, Central Texas flood death toll climbs to 51

Officials in Central Texas say they don’t have an accurate count of the number of people missing after catastrophic flash floods swept through the Guadalupe River corridor on Friday.

Texas flooding latest: Two sisters among 51 dead as desperate search for campers swept away enters third day

Donald Trump described the flooding as ‘terrible’ as emergency services search for dozens of missing children

Four girls missing from a summer camp were found dead as a desperate search for dozens of other campers continues after devastating floods hit Texas, killing at least 51.

At least 15 children were killed as a result of what Texas GOP Congressman Chip Roy called a “once-in-a-century flood.” More than 850 people from around the region have been rescued or evacuated, officials said Saturday.

Two girls — 13-year-old Blair and 11-year-old Brooke — were among those killed by the floods, their father told CNN on Saturday night. Harber said Blair “was a gifted student and had a generous, kind heart,” and described Brooke as “like a light in any room, people gravitated to her and she made them laugh and enjoy the moment.”