Power outages could last weeks in some parts of Houston after deadly thunderstorms with hurricane-force winds caused extensive damage Thursday night, killing at least four people and knocking out electricity to nearly 1 million homes and businesses.

Harris County Judge Lina Hidalgo said it could take weeks to restore power to areas where large transmission towers were toppled by the storm.

“We are going to have to talk about this disaster in weeks, not days,” said Hidalgo, the county’s top elected official, at a news conference Friday morning.

Hidalgo said there were at least 10 large towers that were crumpled by the storm and that getting them back online would take weeks.

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“The next few days are going to be hard. The next few weeks are going to be hard for some folks in our community. They’re going to be uncomfortable. But, we’ve been through this. Our first responders have been through this. This was an unlikely scenario but here we are and we’re nothing if not resilient.”

On Friday morning, power remained out to approximately 800,000 customers after being out to nearly 1 million customers overnight.

Houston Mayor John Whitmire said four, and possibly five, people were killed when storms swept through Harris County, which includes Houston. Officials warned residents that it would be a slow cleanup and that some residents should brace to be without electricity for days, if not longer.

“It was fierce, it was intense, it was quick and most Houstonians didn’t have time to get themselves out of harm’s way,” Whitmire said.

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Whitmire urged people to stay home Friday and to avoid the roads. He said 2,500 traffic lights were out and that there were hazards and debris on roads that made driving dangerous.

Whitmire said mutual aid from surrounding communities and across the state has been remarkable and he thanked Texans for collaborating in their recovery.

“Quite frankly, I’m proud to be the mayor of Houston today. We’re showing again the fine qualities and the unity that we exhibit during these difficult times,” Whitmire said. “We’re doing everything we can. Be patient. Use common sense. Be kind to your neighbors, your family, your pets.”

The mayor warned would-be looters that “police are out in force including 50 state troopers sent to the area to prevent looting.”

STORMS CAUSE WIDESPREAD DAMAGE, KILLING AT LEAST 4

The widespread destruction brought much of Houston to a standstill as crews raced to restore power and remove uprooted trees and debris. School districts in the Houston area canceled classes for more than 400,000 students and government offices were closed. City officials urged people to stay off roads, many of which were flooded or lined with downed power lines and malfunctioning traffic lights.

Whitmire called downtown “a mess” on Thursday and told people not to go to work Friday unless they were considered essential workers.

At least two of the deaths were caused by falling trees and another happened when a crane blew over in strong winds, officials said. Whitmire said wind speeds reached 100 mph (160 kph) “with some twisters.” Whitmire said the powerful gusts were reminiscent of 2008’s Hurricane Ike, which pounded the city.

Hundreds of windows were shattered at downtown hotels and office buildings, with glass littering the streets below. Fallen trees, power lines and broken glass have made some areas impassable, the city said. The state was sending Department of Public Safety officers to secure the area.

The storms weren’t over Friday. Gulf Coast states could experience scattered, severe thunderstorms with tornadoes, large hail and damaging winds. Heavy to excessive rainfall is possible for eastern Louisiana into central Alabama, the National Weather Service said. Flood watches and warnings remained Friday for Houston and areas to the east.

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The powerful storms also struck neighboring Louisiana on Thursday and left more than 215,000 customers without power at their peak. More than 100,000 Entergy Louisiana customers in the New Orleans area lost power, NOLA.com reported.

The Storm Prediction Center’s website showed a report of a tornado in Convent, Louisiana, about 55 miles (89 kilometers) from New Orleans, with multiple reports of trees and power poles down.

A suspected tornado hit the Romeville area of St. James Parish on Thursday night with some homes impacted and trees down, but no injuries or fatalities had been reported, parish officials said in a social media post on Friday morning.

There were wind gusts of 84 mph (135 kph) at Louis Armstrong New Orleans International Airport and 82 mph (132 kph) at New Orleans Lakefront Airport, according to Tim Erickson, a meteorologist at the weather service’s office for New Orleans and Baton Rouge.

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The office for New Orleans and Baton Rouge issued a flash flood warning through Saturday.

Back in Houston, at Minute Maid Park, home of the Houston Astros, the retractable roof was closed due to the storm. But the wind was so powerful it still blew rain into the stadium. Puddles formed on the outfield warning track, but the game against the Oakland Athletics still was played.

Flights were briefly grounded at Houston’s two major airports. Sustained winds topping 60 mph (96 kph) were recorded at Bush Intercontinental Airport.

The power outage numbers were slowly improving Friday morning, down to about 773,000 in Texas and 97,000 in Louisiana, according to Poweroutage.us. At one point, Texas had more than 900,000 outages.

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CenterPoint Energy warned customers in the Houston area to “be prepared for extended weather-related power outages.”

The problems extended to the city’s suburbs, with emergency officials in neighboring Montgomery County describing the damage to transmission lines as “catastrophic” and warning that power could be impacted for several days.

Heavy storms slammed the Houston area during the first week of May, leading to numerous high-water rescues, including some from the rooftops of flooded homes.