HOUSTON — Flash floods swept through south-central Texas early Friday, killing at least 13 people and leaving over 20 summer campers missing, officials said.

Kerr County Sheriff Larry Leitha confirmed 13 fatalities, warning the toll could rise. Lieutenant Governor Dan Patrick said some victims were children and about 23 girls from Camp Mystic along the Guadalupe River were still unaccounted for after the river rose 26 feet in just 45 minutes.

“They may just be stranded and out of contact,” Patrick noted, citing the camp’s message reporting catastrophic flooding, no power, water, or Wi-Fi.

Floodwaters inundated homes, roads, and campgrounds after heavy overnight rain dumped 12 inches — a third of Kerr County’s annual average. Videos showed trees and houses swept away as rescue crews worked nonstop, aided by 500 personnel, helicopters, and the National Guard.

Governor Greg Abbott shared dramatic footage of a victim rescued from a tree, pledging, “We will not stop until everyone is accounted for.”

Authorities warned more rain was expected, calling the floods a “mass casualty event” and urging residents near the Guadalupe River to move to higher ground. Kerr County Judge Rob Kelly called the area “the most dangerous river valley in the United States.”

In June, floods in nearby San Antonio killed at least 10 following torrential rains.