Houston was in "recovery mode" Friday morning after a storm system battered the area overnight, killing at least four people, smashing windows, and toppling trees before it is set to wreak more havoc in the Southeast, bringing a risk of hail, damaging wind, and tornadoes to the area over the weekend.

Houston woke up to scenes of destruction on after severe storms with winds of up to 100 mph spewed debris across roads, and littered the ground downtown with broken glass. Houston Mayor John Whitmire said four people died in the storm, and authorities were investigating unconfirmed reports of a fifth death.

"We're in recovery mode," Whitmire said.

In a news conference on Thursday evening, Houston Fire Chief Samuel Peña said two of the deaths were caused by falling trees, while a third person died in a crane accident.

Mary Benton, spokesperson for the mayor, told USA TODAY the Harris County medical examiner's office would identify those killed and determine the cause of death.

Harris County Judge Lina Hidalgo said on Friday that it would take time to assess the storm's effects, which she said knocked out the power supply for 740,000 customers, most of them residents of Harris County.

"We don't know the extent of damage yet," she said. "We don't know the timeline for electricity restoration. We don't know, again, the exact number of fatalities or injuries."

According to Hidalgo, a tornado formed in Bridgeland, an urban development in Cypress, a suburb about 30 miles northwest of downtown Houston.

"This kind of wind is something we have not seen in Harris County since Hurricane Alicia in 1983," she said.

Hidalgo said she had signed a disaster declaration on Friday morning and Houston's government was in contact with the White House. "We expect the federal government will place utmost attention on Governor Abbott's request to receive resources from federal partners as quickly as possible," she said.

As of Friday morning, debris had been cleared from freeways, but debris was still scattered over individual neighborhoods, Hidalgo said.

On Thursday night, Whitmire urged residents to continue to stay home amid the dangerous road conditions. Widespread power outages had also knocked out traffic lights across the city, posing traffic control hazards for morning commuters. Whitmire said officials were also "concerned" about the dangers of broken glass on roadways.

"Downtown is a mess. It's dangerous due to the glass and the lack of traffic lights," he said. "So stay at home. I can't emphasize that, repeat that enough."

More:How do thunderstorms form? Here's what's actually happening during severe weather.

Peña also warned residents to keep off the roads. "Some areas are without any power, no light. It's hard to see as you're driving," he said.

He said the majority of emergency calls to the fire department were to report downed wires and gas leaks. "If you're smelling gas inside your home, it could be potentially hazardous. So please call 911 if there is a smell of gas, but do so outside of that building," he said.

The National Weather Service was investigating reports of two unconfirmed tornadoes, one in Bridgeland, a suburb around 30 miles northwest of downtown Houston, and another in Galena Park, about 11 miles east of downtown, NWS meteorologist Jeff Evans said on Friday. "The majority of this damage is straight line winds," he said.

More than 900 customers of the utility company CenterPoint Energy had lost their power, he said. Power restoration would take up to 48 hours for some residents. The company said on X that restoring full power would be a "days-long restoration effort."

More than 420,000 outages, or 20% of all power accounts, were reported in the Houston area as of Friday morning, according to USA TODAY's national power outage tracker.

Houston's metro service said on Friday that shuttles would service the Purple and Green train lines due to power outages and debris on the tracks. Morning commuters should expect travel delays.

Schools throughout the area shuttered their doors in response to the severe weather. Whitmire also asked employers in the downtown area to allow their employees to work from home.

By Friday morning, the risk of severe weather in Houston was marginal, with cloudy skies and a few showers expected in the afternoon, according to the Weather Channel.

The storms come weeks after the Houston area faced floods after a bout of heavy rain and thunderstorms earlier this month. In late April, Groveton and Trinity, two towns around 100 miles north of Houston, received a respective 10 and 9 inches of rain.

More:Four dead after severe storms lash Texas; tornadoes, floods loom in Southeast U.S.

Storms to bring hail, rain, possible tornadoes to Southeast

But the storm system is set to bring severe thunderstorms and excessive rainfall to the lower Mississippi Valley and Alabama on Friday and through the weekend.

"If you like rain and storms the next 2 days are for you," the National Weather Service in Birmingham posted on X on Friday morning. Southern Alabama, including Montgomery and Selma, could see a few tornadoes as the area is hit with hail and "damaging winds" of up to 60 mph.

As the storm moves eastward, northeastern Texas and parts of Alabama and Florida could be inundated with up to 8 inches of rain, potentially triggering serious flooding, according to AccuWeather.

Through that night, areas in Mississippi, Louisiana, and Alabama could be at risk of flash flooding, the Weather Channel reported. Amid damaging winds on Saturday, the area faces an isolated tornado threat.

"Gusty winds and hail" would be the main threats in strong storms expected to hit parts of Southeast Mississippi, according to the weather service in Mobile.

Parts of Florida also endured heavy wind on Friday morning – the southern coast near Tallahassee was hit with wind gusts of up to 70 mph, the weather service reported.

Further south, temperatures hit record highs earlier this week. On Wednesday, a heat index of 115 degrees in Key West tied the area's all-time record, AccuWeather reported.

The same day, Miami temperatures hit 96 degrees, just two degrees below its record high for the month. The weather service warned that the city could see its heat index enter the "triple digits" over the weekend.

Cybele Mayes-Osterman is a breaking news reporter for USA TODAY. Reach her by email at [email protected]. Follow her on X @CybeleMO.