The flood waters from Tropical Storm Harvey are beginning to drop across much of the Houston area, emergency officials said.
"The water levels are going down. And that's for the first time in several days," said Jeff Lindner, a meteorologist with the Harris County Flood Control District.
The number of confirmed deaths rose to 20 when authorities reported that two men died in separate drownings. One of them drove around a barricade and into standing water on Monday, while the other tried to swim across a flooded road.
Authorities expect the death toll to rise as the waters recede and they are able to take full stock of the destruction wrought by the catastrophic storm.
Some neighbourhoods were still in danger of more flooding. Mr Linder said a barricade along Cypress Creek in the northern part of the county could fail and swamp an area where some residents ignored a mandatory evacuation order.
The water in two reservoirs that protect central Houston from flooding was likely to peak on Wednesday at levels slightly below those that were forecast, officials said.
Meanwhile, the Texas community of Port Arthur found itself increasingly isolated as Harvey's rains flooded most major roads out of the city and swamped a shelter for victims fleeing the storm that ravaged the Houston area.
The crisis deepened in the coastal city after Harvey rolled ashore overnight for the second time in six days, this time hitting south western Louisiana, about 45 miles from Port Arthur.
Jefferson County sheriff's Deputy Marcus McLellan said he was not sure where the 100 or so evacuees at the civic centre in Port Arthur would be sent.
"People started coming to the shelter on Monday," Mr McLellan said.
"And now it's just all the rainfall that's coming in, and there's a canal by there also that's overflowing."
Some 13,000 people have been rescued in the Houston area, and more than 17,000 have sought refuge in Texas shelters.
With the water still high in places and many hard-hit areas still inaccessible, those numbers seemed certain to increase.
Harvey initially came ashore as a Category 4 hurricane in Texas on Friday, then turned and lingered off the coast as a tropical storm for days, inundating flood-prone Houston, the nation's fourth-largest city.
Early on Wednesday, Harvey returned, coming ashore near Cameron, Louisiana, and bringing with it 45 mph winds and a heavy dose of rain.
Houston's largest shelter housed 10,000 of the displaced - twice its initial intended capacity - and two additional mega-shelters opened on Tuesday for the overflow.
Louisiana's governor offered to take in Harvey victims from Texas, returning a favour after Hurricane Katrina in 2005.
And televangelist Joel Osteen opened his 16,000-seat Houston megachurch after he was blasted on social media for not acting to help families displaced by the storm.
Houston has asked the Federal Emergency Management Agency for more supplies, including cots and food, for an additional 10,000 people, said Mayor Sylvester Turner.
In Port Arthur, Sheriff Zena Stephens told KFDM-TV that authorities were struggling to rescue residents from the flooding.
Mayor Derrick Freeman posted on his Facebook page: "city is underwater right now but we are coming!"
He also urged residents to get to higher ground and to avoid becoming trapped in attics.
Harvey is expected to weaken as it heads through Louisiana and makes it way northward - with Arkansas, Tennessee and Missouri on alert for flooding in the next couple of days.
"Once we get this thing inland during the day, it's the end of the beginning," said National Hurricane Centre meteorologist Dennis Feltgen.
"Texas is going to get a chance to finally dry out as this system pulls out."