Hundreds of people, including young campers, were rescued across Missouri Friday as flash flooding from a once-in-a-millennium deluge transformed rivers into raging torrents.

A series of thunderstorms dumped between 6 and 12 inches of rain across southeast Missouri in what officials have described as a 1-in-1000-year rainfall event. The historic overnight downpour prompted Gov. Mike Kehoe to declare a state of emergency and activate one of the state’s largest search and rescue efforts.