At least 20 girls are missing from an all-girls Christian summer camp in South Texas after catastrophic floods struck the area in the wake of severe overnight storms.

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.

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