Floodwaters have deepened across much of Texas as storms dumped almost another 12in of rain on the Houston area, stranding hundreds of motorists in the fourth-largest US 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 in central Texas – bringing to 17 the number of people killed by the holiday weekend storms in Texas and Oklahoma.
Similar search efforts unfolded just south of the Mexico border where crews tried to track down the missing and assess the damage in the city of Ciudad Acuna after a tornado killed 13 people on Monday.
In Houston, the water rose sharply overnight as about 11in of rain fell, much of it in a six-hour period, but by yesterday evening most rivers had receded back within their banks.
The floodwaters affected virtually every part of the city and paralysed 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 co-ordinator.
The drenching weather threatened to linger. The National Weather Service forecast a 20% to 40% 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 the city centre was backed up for miles, and a handful of motorists travelled the wrong way on the highway to retreat from high water.
Some motorists were stuck on I-45 all night, sleeping in their cars until the backup was cleared about 8am.
Basketball fans at the Toyota Centre, where the Houston 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 severe weather.
The game ended before 11pm but about 400 people were still in their seats at 1.30am, choosing to stay in the building rather than brave the flooded roads outside. Up to 150 people stayed all right, according to arena officials.
A spokeswoman for the district of Harris County, which includes Houston, said up to 700 homes sustained some level of damage.
Some of the worst flooding in Texas was in Wimberley, a popular tourist town along the River Blanco in the corridor between Austin and San Antonio.
The “search component” of the mission ended on Monday night, meaning no more survivors were expected to be found, said Trey Hatt, a spokesman for the Hays County Emergency Operations Centre.
Eight people missing from the destroyed house were friends and family who had gathered for the holiday, said Kristi Wyatt, a spokeswoman for the City of San Marcos. Three children were among the missing.
The Blanco crested above 40ft – more than triple its flood stage of 13ft. Rescuers used pontoon boats and a helicopter to pull people out.
Hundreds of trees along the Blanco were uprooted or snapped, and collected in piles of debris up to 20ft high.
In Ciudad Acuna, mayor Evaristo Perez Rivera said 300 people were treated at local hospitals after the twister, and up to 200 homes had been completely destroyed in the city of 125,000 across from Del Rio, Texas.