The most urgent alerts came in the middle of the night.

In Kerrville, some people huddled inside a church’s activity center, and others looked distraught, shivering under blankets. Brian Eads, 52, was hoping for information about his wife, Katherine, after aggressive floodwaters ravaged their trailer at around 3:30 a.m.

“I have no idea if she’s made it,” Mr. Eads said. “We both got swept away, and then I lost her.”

The couple were awakened by rushing waters, and managed to escape with a man driving a recreational vehicle. But the water caught up with them about 20 feet away, Mr. Eads said, and the vehicle’s engine died. Both he and his wife were swept underwater. He tried to swim toward her voice, he said, but lost her when he was struck in the head by debris. He survived by holding onto a tree and making his way to dry land.

Outside Ingram Elementary School, about seven miles west of Kerrville, people hoped to find missing loved ones, including girls who were staying at Camp Mystic nearby. Some hugged each other outside the main entrance, while others stood waiting to hear from their relative.

Randy Bush, 59, said he had not heard from his fiancée Charlotte Huff, 55, since last night. He had already been at a local Walmart, where others were searching for relatives.

“I have no idea what happened to her,” he said.

His fiancée lives at an R.V. park in the Kerrville area. As soon as he heard about the floods, he rushed to the park, but was stopped by road closures and emergency vehicles.

“When I was there this morning, they were doing water rescues with helicopters,” Mr. Bush said. “From what I saw that park was gone,” he added as he made his way to the school. “It was just all water. It didn’t look like there was anything there. That whole park was done.”

Parents of campers were hoping for the best Friday afternoon. Betty Gerlach, whose 14-year-old grandson is a camper at Camp La Junta, a boys camp about five miles along the river from Camp Mystic, said the boys camp had informed families that all campers were safe and fed. But an evacuation plan was still in development, and would not begin until at least 7 p.m. local time on Friday.

The camp asked families from Houston, the Dallas-Fort Worth area and out of state to begin traveling to the area. But families in nearby Austin and San Antonio were told to “stay put for now,” to avoid overcrowding.

With several camp building washed away in the flooding, the campers had taken shelter in two small cabins while they waited for evacuation, Ms. Gerlach said.

By midafternoon, emergency crews had started to bring some of the stranded girls to Ingram Elementary. One man saw his daughter sitting in the passenger seat of an emergency vehicle and ran after it with a smile.