In July 1987, an eerily similar flood struck campers along the Guadalupe River.

In the early morning of July 17, 1987, between 5 and 10 inches of rain fell across the upper Guadalupe River basin, according to the National Weather Service, triggering a massive surge of water that traveled down the Guadalupe River through Ingram, Hunt -- near Camp Mystic -- Kerrville and eventually Comfort.

Evacuating campers and staff from the Pot O’ Gold Christian Camp were trapped and eventually swept away by overflowing floodwaters from the Guadalupe River. Ten campers were killed and 33 people were injured, according to the National Weather Service.

-ABC News’ Julia Jacobo

State emergency personnel are aiding local search and rescue operations "around the clock" as they search for potential survivors in Texas, Gov. Greg Abbott said.

Several areas in central Texas and the Hill Country are still under "a threat of heavy rain with the potential to cause flooding," Abbott said in a statement late Monday.

"Texans are urged to remain weather aware, heed the guidance of local officials, and regularly monitor weather forecasts," he said.

He added, "Texas will remain engaged until every missing person is found and every Texan recovers from this disaster."

Some 20 state agencies have deployed about 1,750 personnel and more than 975 vehicles and pieces of equipment to aid in the search and rescue, according to the governor's office.

Country musician Pat Green said his family "suffered a heartbreaking and deeply personal loss" during the flooding in Central Texas.

His wife, Kori Green, shared on social media that Pat Green’s brother John, his wife, Julia, and their two children remain missing after the Kerrville flood over the weekend.

"We are heartbroken and anxiously waiting for all of them to be found," she wrote.

-ABC News' Olivia Osteen and Peter Charalambous

Sen. Ted Cruz, R-Texas, called the flooding aftermath at Texas' Camp Mystic -- where at least 27 campers and counselors died amid flooding -- "the most horrible thing I've ever seen."

"The water rose 7 and 8 feet … the cabins are cleaned out, all of the furniture has been pulled out by the current," he told Lindsey David on ABC News Live Prime after touring the campground. "It's heartbreaking."

Cruz said his daughters have gone to summer camps in Kerr County, in Texas' Hill Country, for 10 years and said just last week, his wife had picked up their youngest daughter from camp.

For now, the focus remains on search and rescue, Cruz said, but in the coming weeks and months, he said he hopes to take a look at the timeline of exactly what happened and when warnings went out to see if something could have been done better.

"There's no doubt, any one of us, if we had a time machine and we could step in it right now, we would run to those girls' cabins and pull them out of the cabins before the floodwaters rose," he said. "And so it's worth asking, what could have been done differently?"

Cruz, who was on a pre-planned trip with his family in Greece on Friday when the floodwaters rose, said he was working the phones almost immediately, calling the governor, other state officials and even President Donald Trump.

"You know, look, people love to play politics. I was overseas on a family vacation when this happened. I was almost immediately on the phone," Cruz said, adding, "And then I booked a flight and came back."

Cruz said he left Sunday morning and arrived in Texas on Sunday night.