Heavy rain inundated the Houston area with as much as 10 inches of rainfall in just six hours and triggered flash flooding early Monday.
Jeff Lindner, a meteorologist with the Harris County Flood Control District, said that "significant widespread flooding" was reported northwest of Houston. He added that a total of between 12 and 16 inches of rainfall was expected in the area by daybreak.
In a tweet, he warned of a "life-threatening situation" due to flash flooding developing in northwest Harris County. "Stay where you are," Lindner added.
Rosie Torres, a spokeswoman for the Harris County Office of Homeland Security and Emergency Management, said high water rescues had occurred but the number was not immediately clear.
"The situation is pretty serious," Torres added.
Torres' agency advised residents to "stay home and off the roads."
In a statement, it added: "If your home or apartment takes in water, DO NOT LEAVE. You are safer inside your home. Straying into deep or fast moving flood waters means certain death."
Michael Walter, a spokesman for the Houston Office of Emergency Management, said early Monday that "tremendous rainfall" had been reported over western parts of the city.
Videos and images posted online showed cars stranded in flooding and hail in Houston.
The Weather Channel warned that "heavy rain and thunderstorms remain a threat from eastern Texas northward to the Dakotas," adding that "scattered severe thunderstorms may develop in southern Texas through Monday night" with "damaging wind gusts, hail and isolated tornadoes" all being possible.
More severe weather from the early spring around the United States:
March/April, early spring weather around the United States
Flash floods hit Houston area as storm drenches Harris County
Footsteps can be seen on a recently cleared sidewalk during a spring snow storm in Boston, Massachusetts April 4, 2016. REUTERS/Brian Snyder
Fog envelops the Golden Gate Bridge in San Francisco, California, United States April 8, 2016. REUTERS/Kevin Lamarque TPX IMAGES OF THE DAY
Malia Obama's hair flies into the air as a cold wind hits her and U.S. President Barack Obama while descending the steps of Air Force One upon their arrival at O'Hare Airport in Chicago April 7, 2016. REUTERS/Kevin Lamarque TPX IMAGES OF THE DAY
A man carries an umbrella during a rain storm on Wall St. by the New York Stock Exchange in New York April 4, 2016. REUTERS/Brendan McDermid
Falling snow sits on daffodils outside a Newbury Street shop during a spring snow storm in Boston, Massachusetts April 4, 2016. REUTERS/Brian Snyder
Visitors walk along the Tidal Basin to look at cherry blossoms in Washington March 24, 2016. REUTERS/Jonathan Ernst