US President Donald Trump spoke Friday of seeing devastation like he'd never before experienced as he toured parts of Texas hit by devastating flash floods that have left at least 120 people dead, including dozens of children.

The Republican leader and First Lady Melania Trump were in the Hill Country of central Texas to meet first responders, victims' families and local officials, a week after a rain-swollen river swept away houses, camp cabins, cars and people.

"This is a tough one. I've never seen anything like this," Trump said at a roundtable meeting in Kerrville, in the worst-affected Kerr County.

"I've gone to a lot of hurricanes, a lot of tornadoes. I've never seen anything like this. This is a bad one."

Trump lashed out at reporters for questioning authorities' response to the disaster and said he wanted to focus on solidarity with emergency workers and volunteers.

"All across the country, Americans' hearts are shattered," said Trump, speaking at a table draped in a black banner with the message "Texas Strong."

"I had to be here as president. The first lady wanted to be here."

He compared the suddenly rising floodwaters to a "giant wave in the Pacific Ocean that the best surfers in the world would be afraid to surf."

Earlier, the Trumps were met by Governor Greg Abbott near the Guadalupe River in Kerrville, in an area with numerous downed trees and an overturned tractor trailer.

They were briefed by Texas Emergency Management and Kerrville Fire Dept officials, and greeted by 30 or so rescue workers and Coast Guard members.

The search for more than 170 missing people, including five girls who were at summer camp, was in its eighth day as rescue teams combed through mounds of debris and mud.

But with no live rescues reported this week, worries have swelled that the death toll could still rise.

Trump has brushed off questions about the impact of his cuts to federal agencies on the response to the flood, which he described as a "100-year catastrophe" that "nobody expected."

On Thursday, Homeland Security chief Kristi Noem, who was with Trump in Texas, defended the immediate response as "swift and efficient."

But Texas officials have faced questions about why emergency evacuation messages to residents and visitors along the flooding Guadalupe River reportedly were delayed, in some cases by hours.

Trump expressed support for a flood warning system in a telephone interview with NBC News on Thursday. 

FEMA questions

The floods, among America's deadliest in recent years, have reopened questions about Trump's plans to phase out federal disaster response agency FEMA in lieu of greater state-based responsibility.

FEMA began its response to the Texas flash floods over the weekend after Trump signed a major disaster declaration to release federal resources.

But the president has so far avoided addressing questions about its future. Noem insisted FEMA should be "eliminated" in its current form at a government review meeting Wednesday.

Officials in Kerr County, which sits astride the Guadalupe River in an area nicknamed "Flash Flood Alley," said at least 36 children were killed in the disaster at the start of the Fourth of July holiday weekend.

Details have surfaced about reported delays to early alerts at a local level that could have saved lives.

Experts say forecasters did their best and sent out timely and accurate warnings despite a sudden weather change.

ABC News reported Thursday that at 4:22 am on 4 July, a firefighter in Ingram, upstream of Kerrville, had asked the Kerr County Sheriff's Office to alert residents of nearby Hunt to the coming flood.

The network said its affiliate KSAT obtained audio of the call, and that the first alert did not reach Kerr County's CodeRED system for a full 90 minutes.

In some cases, it said, the warning messages didn't arrive until after 10:00 am, when hundreds of people had already been swept away.

The flooding of the Guadalupe River was particularly devastating for summer camps on its banks, including Camp Mystic, where 27 girls and counselors died.

by Danny Kemp