Five people have died in flooding caused by heavy rainfall in the Houston area, while Texas Gov. Greg Abbott issued a state disaster declaration for nine southeast Texas counties Monday, including Harris County.
Rain gauges in parts of Harris County, which includes most of Houston, showed water levels approaching 20 inches since late Sunday night, with slightly smaller amounts elsewhere in southeast Texas as bayous and creeks overflowed their banks.
Harris County Judge Ed Emmett, the county's chief administrator, said two bodies were found in a vehicle shown on traffic cameras driving around barricades and unsuccessfully attempt to navigate a flooded underpass.
In addition, one person, believed a contractor with the city's airport system, was found in a submerged vehicle not far from George Bush Intercontinental Airport. A second person, a truck driver, was found dead in the cab of his rig after encountering high water on a freeway service road.
Harris County Precinct Sgt. Herbert Martinez said crews monitoring the high water on the road saw the man in the 18-wheeler truck drive directly into the water. He says it's possible the driver may have suffered some kind of medical emergency.
Several shelters were established for people forced from their home, and the city has launched a big effort to reach people who may be stranded.
Houston Mayor Sylvester Turner said no area is being ignored and he's committed to responding to everyone in need. He urged people to stay calm, stay home and stay out of the flood waters.
At least 1,000 people taken from apartment complexes in the north part of the city and moved to a shopping mall were being ferried by city buses to a shelter, the mayor said.
Emmett said thousands of homes in the county outside Houston were flooded, many for the first time. At least 450 high-water rescues were conducted, he said.
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A dozen high water rescue vehicles are assigned to an area where there are a number of apartment complexes that have been flooded. The apartment Betty Hernandez lives in is covered with a foot of water.
"It just started raining, getting worse, worse worse," Hernandez said. "Water just started coming up and coming up, and all of a sudden it just went a little bit too high, started coming in the house, over the vehicles, we lost everything."
Houston Flooding in Photos
Some said the response hasn't been enough.
"It's a mess," Robbie Hubbard said. "Got people with nowhere to go right now and I don't think nobody care about it."
Classes were canceled Monday for the Houston Independent School District's 215,000 students. There was no word late Monday on any changes to Tuesday's operations.
Meteorologist Tom Bradshaw said about 70 Houston subdivisions are flooded, as well as parts of Interstate 10.
Gov. Abbott said some taxpayers affected by severe rain and flooding will qualify for an extension to file their federal tax returns that were due at midnight.
Abbott said Monday that his office had been in contact with the IRS about pushing the tax filing deadline for those in areas inundated by heavy downpours.
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The storms were part of a wide weather system that left warnings and watches through Tuesday morning for Houston, Austin, San Antonio, Dallas, Fort Worth, Tyler-Longview and as far east as Texarkana.
Houston, at near sea level and known for its "gumbo" soft soil, is no stranger to flooding from torrential rains, tropical storms and hurricanes. Last Memorial Day, heavy rains caused severe flooding in the southwest parts of the city. Bayous that last year overflowed after 11 inches of rain quickly rose again, putting water in at least 200 homes, the mayor said. They appeared to be receding slightly by Monday evening.
In 2001, Tropical Storm Allison inundated parts of the city by dumping as much as nearly 29 inches of rain, causing $5 billion in damages.
"A lot of rain coming in a very short period of time, there's nothing you can do," Turner said. "I regret anyone whose home is flooded again. There's nothing I can say that's going to ease your frustration. We certainly can't control the weather."
Samuel Brody, director of the Environmental Planning & Sustainability Research Unit at Texas A&M University, last year called Houston "the No. 1 city in America to be injured and die in a flood."
Rice University engineering professor Philip Bedient has worked with the Texas Medical Center on better preparing its facilities for massive rainfall, including the use of a sophisticated weather alert system that gives the medical center extra time to activate gates and doors that block excess rainwater.
Improving the monitoring of specific watersheds and flood-prone areas might give affected residents the extra bit of time they need to save lives and take protective measures.
"We can't solve this flood problem in Houston," Bedient said. "All we can do is a better job warning."
NBC 5's Jocelyn Lockwood contributed to this report.