Rescue personnel grab the hand of a man stranded in rushing water at the northwest corner of Lamar Boulevard and 15th Street, Texas, May 25, 2015. Shoal Creek overflowed its banks and inundated the major traffic artery with rushing water. Several cars were stalled under and near the 15th Street bridge. [Photo/IC]

Thirteen people are confirmed missing due to flooding that hit along the Blanco River, county officials said. The missing are from two families whose vacation home was swept off its foundation in Wimberley, a town about 30 miles (50 km) southwest of Austin. About 30 other people who were previously unaccounted for have been contacted, Hays County officials said.

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, Hays County officials said.

There was no damage estimate available for Texas, 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.

Houston resident Dutch Small, 40, 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," Small told Reuters.

The National Weather Service issued tornado and thunderstorm watches for later on Tuesday and said more rain is expected this week in Texas and Oklahoma.

More than 200 flights had been canceled by early on Tuesday evening 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.

Roughly 100,000 customers lost power throughout the state after the storm due to high winds and rising waters that caused power poles to snap.

In Houston, about 11 inches (28 cm) of rain fell on Monday while parts of Austin were hit by as much as 7 inches (18 cm). Helicopter crews in both cities plucked to safety people who had been stranded in cars and on top of buildings.