Thunderstorms and torrential rain in the United States have triggered deadly flash flooding along the Guadalupe River in south-central Texas, killing at least 13 people and leaving more than 20 girls from a summer camp missing, according to local authorities.

According to Lt. Gov. Dan Patrick, at least 20 children are unaccounted for at Camp Mystic, an all-girls camp of 750 campers. He says this does not mean they've been lost. "They could be in a tree. They could be out of communication. We're praying for all those missing to be found alive," he said.