Rescuers searched yesterday for at least 12 people missing in spectacular flash flooding in Texas and Oklahoma that also left at least three dead.
More heavy rain with potential for additional flooding was forecast.
The raging waters destroyed hundreds of homes and sent cars floating down streets, rolling and bobbing like giant toys.
In the Texas city of San Marcos, residents were ordered to evacuate their homes as flood waters rose menacingly around them, following torrential rain that turned streets into meandering rivers.
Cars and trucks were submerged and people used inflatable lounge chairs to float down the street, in surreal scenes.
As many as 400 homes in the surrounding area were destroyed, authorities said, and San Marcos opened temporary shelters to host residents who could not return home. Texas and Oklahoma
In Texas at least 12 people are reported missing in Texas and Oklahoma said Kharley Smith, emergency response coordinator for Hays County, which includes San Marcos.
She said people were forming their own search parties along the Blanco River, and warned them against this, saying it was dangerous.
"We have local resources, regional and state assets that are actively doing search and rescues. It's not safe for the general public to go down and do those rescue or search operations themselves," Smith told a news conference.
The city council said the river had broken record levels set in the 1920s.
Fire Marshal Ken Bell told CNN that at least one person was confirmed dead and crews were searching for three missing people.
At least two people also died in Oklahoma, which is located to the north of Texas.
A firefighter in the town of Claremore died when he was swept into a storm drain while trying to help a resident in floodwaters, CNN said, and a woman in Tulsa died after her car hydroplaned.
The National Weather Service warned that strong to severe thunderstorms were expected across a large stretch of the central and southern plains toward the Mississippi River Valley.
Meanwhile, at least 11 people were killed yesterday when a tornado tore through a Mexican town along the US border, officials said.
Some 300 houses were damaged by the twister in Ciudad Acuna, the mayor said.
A seven-year-old boy is missing, mayor Lenin Perez said in a tweet.
The tornado was so powerful that big rig trucks were sent flying into the air and landed on houses.
Firefighters and civil protection officials rushed to the town to start searching for survivors among the rubble of ruined buildings.
The tornado lasted just a few seconds in the city of 136,000. Most of the fatalities were people who were out on the street, the mayor said.
TV footage showed destroyed homes, downed telephone poles and cars covered with rubble.
Telephone service to the city has been partially disrupted.