Tropical Depression Harvey weakened as it moved inland over Louisiana on Thursday, leaving behind record flooding that drove tens of thousands from their homes in Texas.
The death toll was rising as bodies were found in receding waters. A new threat came from explosions at a flood-hit chemical plant in Crosby, 30 miles northeast of Houston.
The storm that paralyzed Houston is predicted to be one of the most expensive natural disasters in U.S. history and presents the administration of U.S. President Donald Trump with massive humanitarian and rebuilding challenges.
The storm has killed at least 35 people and forced 32,000 people into shelters since coming ashore on Friday near Rockport, Texas, on the Gulf of Mexico Coast. It was the most powerful hurricane to hit the state in half a century.
The Houston Fire Department will begin a block-by-block effort on Thursday to rescue stranded survivors and recover bodies, Assistant Fire Chief Richard Mann told reporters.
On Thursday Harvey is forecast to move northeast through Louisiana into Mississippi, dumping 4 to 8 inches (10 to 20 cm) of rain, the National Hurricane Center said. Flood watches and warnings extend from the Texas-Louisiana coast into Kentucky.
"Our whole city is underwater," said Port Arthur, Texas, Mayor Derrick Foreman in a social media post where he also broadcast live video of floodwaters filling his home in the city of 55,000 people, about 100 miles (160 km) east of Houston.
Nearly 30 inches (76.2 cm) of rain hit the Port Arthur area, the National Weather Service said.
Beaumont, near Port Arthur, said it had lost its water supply due to flood damage to its main pumping station and residents in the city of about 120,000 people would lose water pressure from Thursday morning.
Fort Bend County ordered a mandatory evacuation on Thursday for areas near the Barker Reservoir, which was threatening to flood. The reservoir is about 20 miles west from Houston. The county did not say how many people would be affected by the evacuation order.
Clear skies in Houston on Wednesday brought relief to the energy hub and fourth-largest U.S. city after five days of catastrophic downpours. The first flight out of Houston since the storm hit boarded on Wednesday evening. Mayor Sylvester Turner said he hoped the port of Houston, one of the nation's busiest, would reopen soon.
Police in Harris County, home to Houston, said 17 people remained missing.
Nearly 200,000 homes and businesses in Louisiana and Texas were without power on Thursday, utilities reported.