Texas flooding updates: Over 130 dead as flash flood threat increases in Texas

President Donald Trump described the flooding in Texas and subsequent deaths as "terrible," adding that he's working with Texas Gov. Greg Abbott to coordinate possible federal aid and to mitigate the damage.

"They don't know the answer yet as to how many people, but it looks like some young people have died," Trump said Friday on Air Force One, referring to the deaths as "shocking."

Asked if the federal government will send federal aid, the president replied, "Oh yeah, we'll take care of it. We're working with the governor."

-ABC News' Emily Chang

A Texas official said the forecast provided by the National Weather Service underestimated the amount of rain that lashed central Texas before devastating flooding.

Nim Kidd, the chief of the Texas Division of Emergency Management, said the original forecast received on Wednesday from the weather service predicted 3 to 6 inches of rain in the Concho Valley and 4 to 8 inches of rain in the Hill Country.

The state emergency operations center began daily briefings Thursday on the potential for flooding.

"But listen, everybody got the forecast from the National Weather Service, right?" Kidd said during a news conference Friday, adding, "It did not predict the amount of rain that we saw."

Helicopters, rescue swimmers and tactical military vehicles have all been put to use to help rescue and evacuate residents of central Texas stranded by floodwaters.

Overall, first responders rescued or evacuated 237 people -- and 167 of those were by helicopter, said Maj. Gen. Thomas Suelzer, the head of the state's National Guard, speaking during a Friday evening news conference.

Gov. Greg Abbott said crews remain in a search and rescue posture Friday night and will continue to work through the night.

The number of people unaccounted for after devastating flooding in central Texas remains unknown, officials said.

Speaking at a news conference, Kerr County Sheriff Larry L. Leitha said officials do not yet know how many people are unaccounted for.

"It was a holiday weekend here," Leitha said. "We have a lot of campers here, and we do not know that number at this time."

He said up to 25 campers with Camp Mystic, a girls' camp along the Guadalupe River, remained unaccounted for.