SAN ANTONIO — A damaging deep freeze that has plagued the South all week showed no sign of relenting Thursday, with frigid temperatures and a fresh line of snowstorms conspiring to inflict more pain on a region already crippled by widespread power outages, contaminated water supplies and treacherously slick roadways.

Through it all, public infrastructure has proved unequal to the challenge of extreme winter weather, leaving millions of people in peril — and at least 47 dead. The imbalance has been most dramatically on display in Texas, where residents have huddled for days in homes lacking heat, while pipes burst around them and food supplies dwindled.

The state’s struggles led House Speaker Nancy Pelosi (D-Calif.) on Thursday to signal the start of a congressional inquiry into the causes for the prolonged outage. Texas officials, meanwhile, indicated that the impact could have been far worse, while acknowledging they were unprepared for the severity of nature’s fury.

Texas officials said that power was restored Thursday to about 2 million homes, leaving just over 300,000 without electricity. More than 13 million Texans were living under boil-water advisories.

“I want everyone to know that all of us in the state of Texas believe it is completely unacceptable that you had to endure one minute of the challenge that you faced,” Texas Gov. Greg Abbott (R) said at a Thursday afternoon news conference. “We will not stop until normalcy is restored to your lives.”

Yet even as Texas began to glimpse some relief, the march of the latest storm — the third this week — spread destruction ever more widely across the region.

In Oklahoma, the extended stretch of extreme cold, coupled with repeated bouts of snow and freezing rain, prompted the governor to seek federal disaster aid — which President Biden granted Thursday. In North Carolina, the governor urged residents to “limit unnecessary travel and prepare for power outages,” which had arrived for more than 10,000 homes as of the afternoon. And across Louisiana and Mississippi, nearly a quarter-million homes were without power, with officials conceding that in a region better known for hurricanes and tornadoes, the winter cold had caught them off-guard.

“This has been a slow-moving disaster,” Mississippi Gov. Tate Reeves (R) wrote in an extended statement posted on Twitter. “We have been in response mode, not recovery, constantly. There has not been a significant break in the freeze — it just keeps coming.”

With more than two-thirds of the Lower 48 blanketed in snow — the highest level in at least 16 years — the harsh weather was having unforgiving consequences.

In Houston, the nation’s fourth largest city, the main food bank was closed because employees couldn’t get there. Meanwhile, pipes were bursting in homes and apartment buildings, causing major damage, as well as a caution that residents should boil their water at least until Monday. City parks employees worked through the night to deliver bottled water to the city’s hospitals.

Volunteer groups are scrambling to deliver food, water and generators to Houston residents, many of whom still lack power in the midst of a crippling storm. (Lindsey Sitz, Spike Johnson/The Washington Post)

As power returned to many Houston neighborhoods, some people ventured out Thursday to restock supplies that had become badly depleted — and that will almost certainly be needed for the days to come.

“We lost power on the first night. It must have been in the 30s inside our house,” said Peregrine Chapman, who was out shopping with her son, Mason, at the 99 Cents Only store. “Now I’m stocking up on things in case they turn off our power again. I heard that the electricity company is going to do that, and it’s supposed to be super cold again tonight.”

Texas’s embattled electric grid manager said Thursday that it had informed electric suppliers overnight Wednesday that they could restore power to those whose service had been intentionally cut amid a statewide energy shortage. But Electric ­Reliability Council of Texas ­(ERCOT) also warned that more than 40,000 megawatts of power generation remained on forced outage because of harsh weather, and that blackouts could return.

Transmission owners were working to turn the lights back on, the operator said, but “some level of rotating outages may be needed over the next couple of days to keep the grid stable.”

ERCOT has come under sustained criticism for its handling of this week’s weather, in part because the blackouts disproportionally affected some, who have faced days with no power, while leaving others relatively unscathed.

But the operator, which manages supplies to 26 million households across Texas, said Thursday that the situation could have been far worse: Without the rolling blackouts, chief executive Bill Magness told reporters, the entire energy grid could have collapsed. Magness said such a catastrophic breakdown was only minutes — or seconds — away when power plants began seizing up Sunday night.

“It needed to be addressed immediately, and that’s what the operators did,” Magness said.

The council has also been loudly criticized for its lack of preparation for cold weather — a subject that Pelosi hinted will be central to an investigation by the House Energy and Commerce Committee that is expected to be launched next week. Pelosi called Texas’s energy woes “in many ways predictable.”

ERCOT had insisted earlier this winter that it was prepared for whatever conditions the season might bring.

But Magness said Thursday that those preparations were based on the state’s experience during a 2011 cold snap, which until now was the worst the state had seen in recent memory. The National Oceanic and Atmospheric Administration began warning on Feb. 5 that the upcoming wintry surge would be worse — and it was.

“This one changes the game,” Magness said. “It was so much bigger, so much more severe.”

That explanation did little to satisfy Abbott, who lashed out at the operator.

“Texans deserve answers about why these shortfalls occurred, and how they are going to be corrected,” Abbott said. “And Texans will get those answers.”

Abbott sidestepped questions as to whether he shared any of the blame for the hardship Texans have experienced this week.

Texas was not the only state caught unaware. In Oregon, where the storm that has crippled the southern United States levied its first strike nearly a week ago, more than 100,000 people were still without power Thursday. More than half were in the Portland metropolitan area, with service expected to return for nearly all customers by Friday night.

With snow cover in 49 out of 50 states — only Florida has been spared — parts of the country found themselves grappling with conditions that many had seldom seen.

Northwest Louisiana, for instance, had more snow cover Thursday than large parts of Maine. In Mississippi, ice accumulating on trees and power lines from a storm overnight had caused significant power outages. “We have not experienced a winter storm of this magnitude in over 25 years,” said Entergy Mississippi.

Even as crews raced to restore service, officials warned that some Mississippi residents and businesses could be without power into early next week. Utility crews from Arkansas had been called in to help with the restoration effort — although they were having to contend with icy roads to help their neighboring state.

Because of cracked pipes, nearly a million people in Louisiana did not have access to clean and safe drinking water, Gov. John Bel Edwards (D) said at a news conference Thursday.

More than a quarter million were suffering from pumped water outages, Edwards said. The rest were under advisories to boil any tap water before consuming it after winter storms and record low temperatures severely damaged the state’s water infrastructure. Particularly hard hit were areas of the rural west and north that were still recovering from a hurricane six months ago.

In Lake Charles, La., officials are grappling with water issues despite the city’s six plants supplying twice the amount of water normally needed on winter days. The reason was frozen pipes that have burst open on nearly 1,000 vacant properties.

“We’re putting air into the tire, but there are hundreds if not thousands of holes in that tire,” Mayor Nic Hunter said Thursday as temperatures climbed into the 30s. “We’re trying to plug those holes.”

Edwards asked the White House Wednesday night to declare a federal emergency declaration for the state of Louisiana — a request the White House said Thursday it was still considering.

“Jill and I are keeping Texas, Oklahoma, and other impacted states in our prayers,” Biden wrote on Twitter. “I’ve declared states of emergency, authorized FEMA to provide generators and supplies, and am ready to fulfill additional requests.”

As Louisiana waited for possible federal aid, the governor urged Louisianans to try to conserve energy, particularly in the mornings and evenings, as utility companies struggle to make repairs and brace for more cold. “If you’re able, just set your thermostat lower and put on a sweater,” Edwards said.

At least three people in Louisiana have died because of the storm, including two who slipped on ice, and one who died of cold exposure.

In Boyd County, Ky., two deaths have been blamed on hypothermia. One of the deaths involved a 77-year-old woman who lost power, “and her family couldn't get to her or make contact because they were trapped by trees and ice,” coroner Mark Hammond recounted Thursday.

Judge Executive Eric Chaney said he had been up for 50 hours straight, helping to clear over 1,000 trees that cover county roads. Gov. Andy Beshear (D) has called in the Forestry Department and National Guard to help and to rescue stranded residents. Both also conduct wellness checks, especially in a part of the county where residents don’t have cell service or landlines.

With temperatures below freezing, organizations that help the homeless in Mississippi’s capital, Jackson, were rushing to keep the death toll from rising.

Via text thread, organizers and volunteers identified more than 200 homeless on the city’s streets, who were then picked up and taken to locations with heat and power.

“It’s a life-or-death matter because of the conditions outside,” said Jill Buckley, executive director for Stewpot Community Services. “That’s why we’re trying to pull out all of the stops to find people.”

Hoffman reported from Houston. Witte and Hauslohner reported from Washington. Silvia Foster-Frau in San Antonio; Austyn Gaffney in Louisville; Sarah Fowler in Jackson, Miss.; Hannah Knowles, Paulina Villegas, Matthew Cappucci, Donna Cassata, Mark Berman, John Wagner and Derek Hawkins in Washington contributed to this report.