HOUSTON (Reuters) - Houston strained under the arrival of tens of thousands of people at city shelters fleeing submerged homes and flooded roads on Wednesday, while some incidents of looting and armed robberies forced a midnight curfew.

City and regional officials showed signs of tension after working nonstop for a week or more on storm preparations and response, with Houston Mayor Sylvester Turner bluntly telling the U.S. Congress to quickly approve aid for victims of Tropical Storm Harvey.

The storm that came ashore on Friday near Corpus Christi was the most powerful hurricane to hit Texas in more than 50 years. It has killed at least 25 people and forced 30,000 people to flee to emergency shelters. Damage has been estimated at tens of billions of dollars.

The Houston City Council voted on Wednesday to allocate $20 million to storm recovery efforts, pulling the money from a rainy day fund, though that is an initial step and far more will be needed, officials said.

Texas Governor Greg Abbott said the state could need federal relief topping $125 billion, saying the region should get more than the amount Congress approved for Hurricane Katrina victims in 2005.

In Houston, police and other first responders have transitioned from rescue operations back to law enforcement, with Harris County District Attorney Kim Ogg vowing to vigorously prosecute looters. At least 40 have been arrested for looting, including one person who allegedly drove a sport utility vehicle into a cash machine, Ogg’s office said.

The surge in evacuees has been stressing resources in the fourth-largest U.S. city. As of Wednesday morning, Texas officials said close to 49,000 homes had suffered flood damage, with more than 1,000 destroyed. Thousands of other homes were threatened by two reservoirs swollen by as much as 52 inches (132 cm) of rain in some areas.

Officials ordered evacuations in several areas around levees or dams, but opted not to call for a mass evacuation, which could have led to chaos during the storm.

As Harvey began to dump rain and cause flooding, the city opened the George R. Brown Convention Center last weekend. It planned to house 5,000 people, operating with the help of American Red Cross volunteers and others. The center’s population quickly grew to double that capacity, as people streamed in from areas south and west of Houston.

At least one man was arrested in the convention center on Thursday after he tried to steal a cot and insulted police officers, according to video posted on social media.

Officials opened two more “mega” centers late Tuesday at the Toyota Center, home of the National Basketball Association’s Houston Rockets, and NRG Park, part of the complex that hosted the 2017 Super Bowl.

As police responded to scattered incidents of looting and armed robberies, the mayor ordered a curfew from midnight to 5 a.m., which residents respected. There were no arrests for curfew violations on Tuesday night, police said.

There were at least 17 missing people as of Wednesday afternoon in Harris County, and a family of six, including four children, drowned inside a van in Houston during the storm, law enforcement officials said.

Evacuees take shelter from Tropical Storm Harvey in the George R. Brown Convention Center in Houston, Texas, U.S. in this August 28, 2017 handout photo. Texas Military Department/Handout via REUTERS

Houston Police Chief Art Acevedo said would-be looters impersonating police officers knocked on doors in at least two parts of the city telling residents to evacuate their homes.

“There’s still some significant threats out there,” Acevedo told a special session of the Houston City Council on Wednesday.

Late Tuesday, Harris County officials opened the shelter at NRG Park, which can house 10,000, and will be staffed in part by members of the National Guard.

When a levee broke on Tuesday morning in Brazoria County south of Houston, the county’s chief administrator urged residents to “get out now.”

Mandatory evacuation orders covered Brazoria, Galveston and Fort Bend counties south and west of Houston, and officials issued calls for others to leave voluntarily.

On Wednesday afternoon, about 8,000 were at the nearly 2-million-square-foot Houston convention center, which had hosted evacuees in at least three prior storms. The population had dipped somewhat as other centers opened and some evacuees moved on.

A long-term solution for evacuees has yet to be formulated, officials said.

“Right now we’re just working in 12-hour increments,” said Tom McCasland, Houston’s housing and community development department director and head of the convention center shelter.

Some criticized the decision not to order a mass evacuation, but officials noted that a 2005 evacuation ahead of Hurricane Rita turned into a nightmare for many in Texas and Louisiana who became trapped in vehicles that ran out of fuel on clogged roadways.

Area churches and aid organizations donated clothing, bedding and food for evacuees. The Red Cross brought at least 1,000 volunteers to staff the convention center, and provided cots, blankets and food for 34,000 across the region, officials said.

Turner, the mayor, called on the Federal Emergency Management Agency to send cots, food and other supplies, as well as send staff directly into damaged communities, not just into shelters.

“I can’t think of one district where there are not tremendous needs,” said Turner. “People are looking for results.”