In the US state of Texas, at least 11 people were killed in the Dallas area over the weekend as floods and tornadoes flattened buildings and disrupted transport for millions.
Rescue operations were underway in several counties where people had been trapped in cars.
Emergency workers conducted dozens of water rescues and evacuated residents from homes.
Tornado watches and warnings have been issued for parts of Texas as well as Louisiana, Oklahoma, Arkansas and Mississippi.
Officials estimated some 800 homes have been damaged in the Dallas metropolitan area. Scores of people were injured in the region, home to about seven million residents.
The governor of Missouri to declare a state of emergency in his state.
He said at least eight people had been killed and numerous roadways had been closed.