Claire Taylor and John Bacon

USA TODAY NETWORK

HOUSTON — Nearly all waterways in and around the city had crested and floodwaters were slowly receding Wednesday, but the region faced an enormous task to emerge from the devastation of Harvey, which the National Hurricane Center announced Wednesday night was downgraded from a tropical storm to a tropical depression.

The good news on water levels came hours after the storm made a second landfall, slamming coastal Louisiana not far from the Texas border. And although the rain had stopped in Houston, the east Texas city of Port Arthur was hit so hard a shelter was flooded and had be evacuated.

"Our whole city is underwater right now," Port Arthur Mayor Derrick Freeman, whose own home was swamped by three feet of water, said in a Facebook post Wednesday. The city was pleading for more boats to aid in rescues.

Harvey's impact was far from over. The storm, which first hit the Texas coast Friday as a strong hurricane, was forecast to drop up to 10 inches of rain on Louisiana before moving on to Arkansas, Tennessee and parts of Missouri. Forecasters warned of possible tornadoes across a wide swath of the Southeast as Harvey rolled inland.

“We are working with the state of Louisiana as the storm moves through their state,” Elaine Duke, the acting secretary of Homeland Security, said at a Washington news conference. She also warned that, despite receding waters in Houston, "catastrophic flooding is likely to persist days after the rain stops.”

The confirmed death toll was in double-digits, including six family members whose bodies were found Wednesday in a van that disappeared in high water three days earlier.

"We are sad to confirm we have retrieved six victims from a van that was submerged in Greens Bayou. #harvey," the Harris County Sheriff's Office tweeted.

Authorities were concerned that more bodies would be found when the water recedes.

AccuWeather estimated Harvey's cost at $160 billion, making it the costliest natural disaster in U.S. history. AccuWeather president Joel Myers called Harvey a "1,000-year storm" and said parts of Houston will be uninhabitable for weeks or months.

More:Harvey to be costliest natural disaster in U.S. history, with an estimated cost of $160 billion

More:Texas mom dies saving her infant daughter during Hurricane Harvey flooding

Some areas near Houston received more than 50 inches of rain, more than the level usually seen in a year. The storm was not expected to bring the devastating flooding seen here to Louisiana and other states, but flash flooding could occur, AccuWeather reported.

FEMA Administrator Brock Long said more than 30,000 people took refuge in more than 200 shelters, large and small, in Texas. About 1,800 evacuees have been moved to hotels and other longer-term housing options, he said.

In Houston, authorities opened two more megashelters — the arena that houses the NBA Rockets and the stadium home of the NFL Texans — after the convention center quickly became packed with almost 9,000 evacuees.

Joel Osteen, pastor of the Lakewood megachurch, and his wife opened the doors of his 16,000-seat arena to evacuees. Osteen was engulfed in a social media controversy after the storm first hit, accused of denying shelter to evacuees.

One sports site that will be used for its intended purpose is Minute Maid Park. The Houston Astros announced Wednesday that they would return to business on Sunday with a three-game series against the New York Mets.

Houston Mayor Sylvester Turner imposed a midnight-to-5 a.m. curfew aimed at ensuring that vacant homes and streets would be safe. Turner and Police Chief Art Acevedo have issued stern warnings that looters would be prosecuted to the fullest extent of the law.

"People were very cooperative last night," Turner said Wednesday. "The curfew will remain in effect until we get past the situation we are in."

Tiffany Duron wasn't convinced. The East Houston resident packed her things and was eager to leave the convention center Wednesday, even though floodwaters had reached her roof line when she and her family fled for the shelter two days earlier.

"They were already breaking into my neighbors'" homes, she said, adding that the looters "are making it worse for everybody."

More than 13,000 people have been rescued from flooded homes. Gov. Greg Abbott said another 10,000 National Guard troops from across the nation would be joining the 14,000 already deployed in the region to provide security and aid in rescue efforts.

Many everyday people have been aiding in those efforts. In West Houston, Joel Moore said he had gone out on search-and-rescue missions with his church, retrieving about a dozen residents. “It’s a constant anxiety and dread,” he said.

Long said that, once the boats are gone, volunteers will be needed to help clean up homes and provide other services for years. Houston's airports were scheduled to begin limited operations late Wednesday, and some roads were finally clearing — small victories on a long road to recovery.

“This is going to be an incredibly large disaster for the country,” Long said. “The economic cost to measure this disaster, we aren’t going to know the true cost of that for many years.”

Taylor reports for The (Lafayette, La.) Daily Advertiser; Bacon for USA TODAY from McLean, Va. Contributing: Doyle Rice, Rick Jervis, Bart Jansen and Jane Onyanga-Omara, USA TODAY

More:Harvey search and rescue: 'Constant anxiety and dread'