Story highlights At least four of the deaths are in Harris County

The Harris County judge says 240 billion gallons of rain has fallen

The forecast calls for rain through late Tuesday

(CNN) At least five people have been killed in flooding that has covered the Houston region, officials said Monday, forcing the evacuation of hundreds of people and knocking out power to thousands of homes and businesses.

"This is a life-threatening emergency," the city said on an emergency website. "Houston residents should avoid travel at all costs today."

Four of the deaths happened in hard-hit Harris County, officials said.

The driver of an 18-wheeler was found dead inside the cab after he drove into high waters, a Harris County constable reported, and another man was found dead in a submerged car, the Houston Fire Department said.

Two others were found dead after driving around a barricade on Houston's west side, Harris County Judge Ed Emmett said.

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