As of Tuesday morning, authorities in the worst-hit Kerr County had recovered the bodies of 87 victims, Sheriff Larry Leitha told reporters.

The deceased include at least 27 girls and counselors who were staying at a youth summer camp on the Guadalupe River over the Fourth of July holiday weekend.

"At present, five Camp Mystic campers and one counselor still remain unaccounted for," Leitha added.

At least 108 flood-related deaths were reported in total across central Texas, according to local officials.

Ben Baker with the Texas Game Wardens said search and rescue efforts involving helicopters, drones and dogs were extremely difficult because of the water and mud.

"When we're trying to make these recoveries, these large piles can be very obstructive, and to get in deep into these piles, it's very hazardous," Baker said.

"It's extremely treacherous, time consuming. It's dirty work, the water is still there."

He added that special attention was being paid to the first responders' mental state, particularly given that the bodies of children were being recovered.

In the town of Hunt, the epicenter of the disaster, an AFP team saw recovery workers combing through piles of debris with helicopters flying overhead, as hopes dimmed for finding any survivors.

Javier Torres, 24, was digging through mud as he searched for the body of his grandmother, after having located the remains of his grandfather.

He also discovered the bodies of two children, apparently washed up by the river.

Officials warned that with more heavy rain forecast, recovery efforts would be rendered even more difficult.

"We've had some reports of maybe some additional water coming in, obviously, that's going to impact the search and recovery efforts," said Baker.

He said the weather may impact aerial patrol patterns, but "it won't deter them."

US President Donald Trump planned to visit Texas on Friday, as the White House slammed critics claiming his cuts to weather agencies had weakened warning systems.

The president, who previously said disaster relief should be handled at the state level, has signed a major disaster declaration, activating fresh federal funds and freeing up resources.