At least 24 people have died after heavy rain pounded Kerr County, Texas, early Friday, leading to "catastrophic" flooding, the sheriff said.

Authorities have said thirteen people have died in Kerr County in the US state of Texas amid a bout of severe weather and flooding. Others remain unaccounted for - including around 20 children who had been at a summer camp.

Rescuers were desperately searching for at least 20 girls missing from a riverside summer camp, officials said Friday, after torrential rains caused a "catastrophic" flash flood that killed at least 24 people as it swept through south-central Texas.