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.

The death toll from devastating floods in central Texas has risen to 24, Kerr County Sheriff Larry L. Leitha told reporters during a news conference Friday evening.

The sheriff did not provide an update on the number of people unaccounted for. Earlier, state officials said about 23 campers with a girls' summer camp remained unaccounted for.

Texas Gov. Greg Abbott said the state remains in a search and rescue posture hours after devastating flooding tore through central Texas.

He said two state search and rescue teams, the Texas National Guard and a host of other agencies are continuing to conduct rescues Friday night.

"They will continue in the darkness of night … They will be nonstop, seeking to find everybody who is unaccounted for," Abbott said during a news conference Friday night.

The governor signed a disaster declaration for the affected counties.