Meteorologists in Arkansas confirmed a tornado touched down in Little Rock and the surrounding area Friday afternoon.
The National Weather Service described the storm as "catastrophic."
Baptist Health in Little Rock said they are preparing for a surge of injuries. They said they treated more than 20 patients Friday afternoon, five of which are in critical condition.
The University of Arkansas for Medical Sciences Medical Center was operating at a mass casualty level and expecting at least 15 to 20 patients from the tornado, spokesperson Leslie Taylor said. Several people had already been transported to the medical center, but an exact count was not immediately available.
Mark Hulsey, a special projects manager for Pulaski County, which includes Little Rock, said at least one person was in critical condition.
The force of the tornado flipped cars, semi trucks -- and at least one bus. Several home and businesses, including a grocery store, were destroyed or heavily damaged.
It is very, very powerful," meteorologists with KATV said.
No one should be outside right now," meteorologists advised shortly before 4 p.m.
Gov. Sarah Huckabee Sanders tweeted that she signed an executive order declaring a State of Emergency.
We will spare no resource to assist with resource and recovery efforts for Arkansans impacted," she wrote on Twitter.
Huckabee Sanders also noted that significant damage has occurred in Central Arkansas and that she has been in constant communication with state police and first responders.
Praying for all those who were and remain in the path of this storm," she wrote. "Arkansans must continue to stay weather aware as storms are continuing to move through."
The Little Rock Fire Department said there is "heavy damage and debris" along Interstate 430 and urged the public to stay off the highway and the surrounding area.
"Rescue operations are being performed so please avoid this area as it may be impossible to pass," the department noted on social media.
KATV meteorologists called it a long-track supercell tornado in their region.
"I'm afraid we aren't done yet," meteorologist Todd Yakoubian advised.
Soon after the tornado hit Arkansas, a tornado touched down near Brooklyn, Iowa.
A video shows a funnel cloud intensify into a tornado on live television.
The footage was captured by KGAN in the middle of a weather report.
A second confirmed twister touched down in Iowa, while damaging hail fell in Illinois. The extent of any damage was not immediately clear.
About 32,000 were without electricity in Oklahoma, where where wind gusts of up to 60 mph fueled fast-moving grass fires. People were urged to evacuate homes in far northeast Oklahoma City, and troopers shut down portions of Interstate 35 near the suburb of Edmond.
More outages were reported in Kansas, Missouri and Texas.
Before the storms hit, meteorologists said the weather had the potential to impact as many as 65 million Americans in at least 15 states across the nation.
Experts said the dangerous spring storm system will hit parts of America’s Midwest and South -- from Texas to Michigan, including areas such as St. Louis, Chicago, Indianapolis, as well as Ohio, Tennessee and beyond.
A severe weather outbreak appears increasingly likely this afternoon/evening across a large portion of the Mississippi Valley," according to the National Weather Service's Storm Prediction Center. "At least a few long-track, strong to potentially violent tornadoes are probable. Swaths of intense damaging wind and very large hail are also expected."
The Storm Prediction Center also noted that a Tornado Watch is in effect until 8 p.m. CDT for parts of the middle and southern Mississippi Valley.
This is a particularly dangerous situation. Several tornadoes (some intense), scattered large hail, and scattered damaging gusts are expected. Stay weather aware in these areas."
A storm threat will then shift to the Northeast on Saturday.
The forecast comes in the wake of deadly storms, as at least 21 people in Mississippi and a man in Alabama were killed during the weekend. The toll was especially steep in Sharkey County, in western Mississippi, where Moore was among 13 people who died in a county of 3,700 residents.
President Joe Biden and Dr. Jill Biden on Friday visited Rolling Fork, Mississippi, which was brutally hit by a tornado. The twister destroyed roughly 300 homes and businesses in the small town and the nearby town of Silver City, leaving mounds of wreckage full of lumber, bricks and twisted metal. Hundreds of additional structures were badly damaged.
Experts advised the public to prepare for the extreme weather and have emergency supplies on hand, such as water bottles, batteries, candles, and ready-to-eat food, in case there are power outages.
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EDITOR'S NOTE: KGAN and The Associated Press contributed to this report.