(CNN) -- [Breaking news, published at 6:55 p.m. ET]

A storm that produced a tornado in the St. Louis area Friday afternoon has left at least four people dead, according to Mayor Cara Spencer.

[Original story, published at 4:02 p.m. ET]

An incredibly dangerous day of severe thunderstorms including the potential for long-lasting, powerful tornadoes and hurricane-strength wind gusts is underway in the eastern half of the United States.

The threat for tornadoes and damaging winds is escalating Friday after the same system already produced destructive storms and tornadoes in the Midwest and Great Lakes Thursday.

It’s all part of a multi-day threat of widespread severe weather that will stretch into early next week.

Here’s the latest:

The atmosphere is supercharging a new round of severe thunderstorms after stormy weather that stretched from Arkansas to Kentucky Friday morning cleared out of the area.

Those morning storms shifted east into parts of the Appalachians in the early afternoon, leaving the door open for explosive thunderstorm development across the Mississippi and Ohio Valleys.

“A regional outbreak of severe thunderstorms is likely this afternoon into tonight,” the SPC warned Friday, adding some people in the path of storms will see “intense supercells.”

More than 70 million people in the eastern half of the US are under at least a level 2-of-5 threat of severe thunderstorms on Friday, but the greatest risk of long-lasting, EF3-plus tornadoes and widespread damaging winds is centered on parts of the Mississippi and Ohio Valleys.

“All severe weather hazards are on the table, including damaging winds, large hail, tornadoes, and torrential rainfall,” the National Weather Service in Louisville, Kentucky, warned. “A few strong tornadoes and instances of very large hail are possible.”

Severe thunderstorms in Missouri and Arkansas in the afternoon were already posing a tornado and hail risk, with additional storms expected to develop from Texas to Illinois. Storms will expand rapidly in scope as they push east. Initial storms are those most likely to become supercells capable of producing tornadoes, damaging wind gusts and large hail.

That threat will continue into the evening before some storms start to form unbroken lines. The wind threat will increase once storms form lines, with gusts stronger than 75 mph and damage possible over hundreds of miles.

Dangerous storms could continue after dark, particularly in parts of Kentucky and areas east. It’s a threat to be especially mindful of as nighttime tornadoes are nearly twice as likely to be deadly as those occurring during the day, a 2022 study found.

At least 11 tornadoes were reported in Minnesota, Wisconsin, Illinois and Michigan as thunderstorms roared through the Midwest Thursday.

Significant damage was reported in Dodge County, Wisconsin, as a cluster of storms around the county prompted shelter-in-place alerts and displaced residents, according to Sheriff Dale Schmidt.

One person was taken to the hospital with injuries in Juneau, the sheriff said Thursday, adding there “may have been another minor injury or two that occurred.”

Many streets and highways in the county are closed due to downed power lines and trees, Schmidt said. Multiple homes in Juneau were damaged and at least one house suffered a roof collapse. Everyone inside was able to get out safely, he added.

Powerful winds also roared through multiple states. A weather reporting station on Lake Michigan near Chicago’s Navy Pier recorded a hurricane-strength wind gust of 79 mph in the evening.

Storms also slammed into Michigan, taking down trees and power lines while damaging homes and businesses.

Multiple areas suffered “structural damage” in western Michigan’s Allegan County, according to the sheriff’s office. Martin Township was among the places impacted: Storms caused “vast amount of damage,” with many downed trees and power lines, though no injuries had been reported as of Friday, according to Martin Township Fire and Rescue. Firefighters responded to 34 calls overnight, the agency said.

More than 300,000 homes and businesses across four Midwest states were still without power Friday afternoon, including more than 200,000 in Michigan, according to PowerOutage.us. Michigan utility company Consumers Energy said assessments on power restoration are still waiting to be made, according to CNN affiliate WNEM.

Severe thunderstorms are possible in the Mid-Atlantic and Northeast on Saturday as the same storm driving Thursday and Friday’s threats pushes east. Damaging wind gusts and hail are the greatest threats for now, but a tornado can’t be ruled out.

New storms could bring damaging wind gusts, hail and tornadoes to parts of the southern Plains starting Saturday afternoon.

The Plains will remain the main focus of severe weather on Sunday and Monday as well, with damaging storms possible in much of Oklahoma and Kansas. The severe thunderstorm threat will then shift back into parts of the Mississippi Valley on Tuesday.

More details about the exact risks these storms will pose and the populations under threat next week will become clear in the coming days.