HOUSTON — Floodwaters deepened across much of Texas on Tuesday as storms dumped almost a foot more of rain on the Houston area, stranding hundreds of motorists and inundating the famously congested highways that serve the nation’s fourth-largest city.

Meanwhile, the search went on for about a dozen people who were still missing, including a group that disappeared after a vacation home was swept down a river and slammed into a bridge.

Several more fatalities were reported — four in Houston and four more in Central Texas. That brought to 17 the number of people killed by the holiday weekend storms in Texas and Oklahoma.

Similar search efforts unfolded just south of the Texas-Mexico border, where crews tried to track down the missing and assessed damage in the city of Ciudad Acuna after a tornado killed 13 people Monday.

In Houston, the water rose sharply overnight as about 11 more inches of rain fell, much of it in a six-hour period. By Tuesday evening, most rivers had receded back within their banks.

The floodwaters affected virtually every part of the city and paralyzed some areas. Firefighters carried out more than 500 water rescues, most involving stranded motorists. At least 2,500 vehicles were abandoned by drivers seeking higher ground, officials said.

“Given the magnitude and how quickly it happened, in such a short period of time, I’ve never seen this before,” said Rick Flanagan, Houston’s emergency management coordinator.

The drenching weather threatened to linger. Forecasts called for a 20 to 40 percent chance of thunderstorms through the rest of the week in Houston.

The flooding closed several highways, and the ones that stayed open became a gridlocked mess.

Interstate 45 near downtown was backed up for miles Tuesday morning, and a handful of motorists traveled the wrong way on the highway to retreat from high water.

Small cars weaved between massive 18-wheelers as other drivers stared at them in disbelief. With no end to the backup in sight, some drivers got off the freeway, only to be held up again by water covering nearby access roads.

In the Heights neighborhood about 5 miles from downtown, groups of people roamed the streets after escaping their stalled cars, and police cruisers blocked some dangerous roads.

Some motorists were stuck on I-45 all night, sleeping in their cars until the backup was cleared about 8 a.m.

NBA fans at the Toyota Center, where the Rockets hosted a Western Conference finals game against Golden State on Monday, were asked with about two minutes left in the game not to leave the arena because of the weather.

The game ended before 11 p.m., but about 400 people remained in their seats at 1:30 a.m., choosing to stay in the building rather than brave the flooded roads that awaited them outside. Up to 150 people stayed all right, according to arena officials.

A spokeswoman for the flood district of Harris County, which includes Houston, said up to 700 homes sustained some level of damage.

Yesenia Lopez and her husband, Armando, waded through knee-deep water, carrying bags of possessions over their heads. During the night, a nearby bayou overflowed and flooded their apartment complex.