The death toll from flash floods that struck central Texas, U.S., on Friday has now climbed to more than 100 people and an unknown number of others are missing.

Search and rescue teams are wading through mud-piled riverbanks as more rain and thunderstorms threaten the region, but hope was fading of finding any more survivors four days after the catastrophe.

Camp Mystic, a Christian all-girls' summer camp, confirmed at least 27 girls and staff were among the dead. Ten girls and a camp counsellor are still missing.

The White House meanwhile rejected suggestions that budget cuts at the National Weather Service (NWS) could have inhibited the disaster response.

At least 84 of the victims - 56 adults and 28 children - died in Kerr County, where the Guadalupe River was swollen by torrential downpours before daybreak on Friday, the July Fourth public holiday.

Some 22 adults and 10 children have yet to be identified, said the county sheriff's office.

Camp Mystic said in a statement on Monday: "Our hearts are broken alongside our families that are enduring this unimaginable tragedy."

Richard Eastland, 70, the co-owner and director of Camp Mystic, died trying to save the children, the Austin American-Statesman reported.

Local pastor Del Way, who knows the Eastland family, told the BBC: "The whole community will miss him [Mr Eastland]. He died a hero."

In its latest forecast, the NWS has predicted more slow-moving thunderstorms, potentially bringing more flash flooding to the region.

Critics of the Trump administration have sought to link the disaster to thousands of job cuts at the NWS' parent agency, the National Oceanic and Atmospheric Administration.

The NWS office responsible for forecasting in the region had five employees on duty as thunderstorms brewed over Texas on Thursday evening, the usual number for an overnight shift when severe weather is expected.

White House press secretary Karoline Leavitt rejected attempts to blame the president.

"That was an act of God," she told a daily briefing on Monday.

"It's not the administration's fault that the flood hit when it did, but there were early and consistent warnings and, again, the National Weather Service did its job."

She outlined that the NWS office in Austin-San Antonio conducted briefings for local officials on the eve of the flood and sent out a flood watch that afternoon, before issuing numerous flood warnings that night and in the pre-dawn hours of 4 July.

Trump, who is expected to visit Texas later this week, pushed back when asked on Sunday if federal government cuts had hampered the disaster response, initially appearing to shift blame to what he called "the Biden set-up", referring to his Democratic predecessor.

"But I wouldn't blame Biden for it, either," he added. "I would just say this is a 100-year catastrophe."

Texas Senator Ted Cruz, a Republican, told a news conference on Monday that now was not the time for "partisan finger-pointing".

One local campaigner, Nicole Wilson, has a petition calling for flood sirens to be set up in Kerr County - something in place in other counties.

Such a system has been debated in Kerr County for almost a decade, but funds for it have never been allocated.

Texas Lt Gov Dan Patrick acknowledged on Monday that such sirens might have saved lives, and said they should be in place by next summer.

Meanwhile, condolences continued to pour in from around the world.

King Charles III has written to President Trump to express his "profound sadness" about the catastrophic flooding.

The King "offered his deepest sympathy" to those who lost loved ones, the British Embassy in Washington said. (BBC)

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