Torrential rains have killed at least 15 people in Texas and Oklahoma, including two in Houston where floods turned streets into rivers and led to about 1000 calls for help in the fourth-most populous US city, officials say.
The death toll is set to rise with numerous people still missing in Texas after the storms slammed the states during the Memorial Day weekend, causing record floods that destroyed hundreds of homes, swept away bridges, and even unearthed a coffin from a Houston cemetery. It washed ashore on the banks of a bayou.
"A lot of folks drove their car into high water and had to abandon those vehicles," Mayor Annise Parker said at a news conference.
Two of the dead in Houston were found in their cars and another was spotted floating in a bayou. The Oklahoma Medical Examiner's office said six people have died in weather-related incidents over the holiday weekend in the state.
Though Parker said parts of the city were unscathed, more than 1000 vehicles were submerged in the Houston floods and people took instead to bicycles, kayaks and surfboards to navigate water-covered streets. The Houston Fire Department brought about 500 people to safety in boats, local media reports said.
"There are still some significant areas of really devastating flooding in Houston," Parker said, adding most of Houston is high and dry but advised people to stay home.
President Barack Obama said today he had assured Texas Governor Greg Abbott that he could count on help from the federal government as the state recovers from the floods. Abbott has declared a state of disaster in 24 Texas counties.
Abbott said he has deployed the state's National Guard and was worried the death toll could rise.
"We still have countless people who are missing," he told CNN.
Twelve people are confirmed missing and about another 30 are unaccounted for due to flooding that hit along the Blanco River in central Texas, county officials said. The missing were from two families whose vacation home was swept off its foundation in Wimberley, a town about 50km southwest of Austin.
Search dogs and boats were being used to search for the missing. The river rose so quickly and with such force, it caused a flood gauge to break, Hayes County officials said.
There was no damage estimate available for the state, which has a $1.4 trillion-a-year economy and is the country's main domestic source of energy as well as an agricultural and manufacturing power.
'It happened so fast'
Houston resident Dutch Small climbed onto the roof of his car when the water came up to his knees inside his vehicle and was eventually rescued by a passing tow truck driver.
"It happened so fast. Every person that died in the flooding, I know what was going through their minds. They didn't measure the threat accurately. They were like me," the 40-year-old said.
More bad weather forecast
More bad weather was expected, with the National Weather Service issuing a flash flood warning today for Houston as a line of thunderstorms moved along the Gulf of Mexico coast toward Florida. It said there was a high chance of more rain and thunderstorms for Texas this week.
One of those killed was an 18-year-old girl whose car was swept away by flood waters as she returned home from her high school prom, police in Devine, Texas, south of San Antonio, said.
More than 170 flights had been canceled at airports in Houston and Dallas - some of the nation's busiest - as blocked roads made it difficult for workers to get to their jobs. A sinkhole also closed a runway at the Dallas/Fort Worth International airport.
About 100,000 customers were without power throughout the state due to high winds and rising waters that caused power poles to snap.
About 28cm of rainwater fell in Houston on Monday, while parts of Austin were hit by as much as 18cm. Helicopter crews in both cities pluck people to safety who had been stranded in cars and on top of buildings.
