The University of Arkansas for Medical Sciences hospital, the region's only major trauma centre, declared a level-1 mass casualty alert after the tornado struck Little Rock, the state's capital and most populous city, on Friday afternoon.
Arkansas Governor Sarah Huckabee Sanders signed an executive order to immediately authorise $US250,000 ($A373,972) from the state disaster response and recovery fund, a local reporter tweeted.
Governor Huckabee Sanders said on Friday two deaths had been reported in Arkansas, with the toll expected to rise.
The twister was spawned by one of the numerous violent thunderstorms raking a vast swathe of the US heartland as part of a much larger expanse of extreme spring weather.
"At this time, we know of 24 people who have been hospitalised at Little Rock hospitals," Mayor Frank Scott Jr said on Twitter.
Separately, Baptist Health Medical Center in the adjoining town of North Little Rock, just across the Arkansas River from the capital, reported treating 11 patients from the storm, one of them in critical condition.Â
Local television station KTHV-TV reported one storm-related death in North Little Rock but that could not be immediately confirmed.
Between five and 10 other people injured by the twister were treated at the emergency department of the Unity Health hospital in nearby Jacksonville, administrator Kevin Burton said.
Television station KAIT8-TV in Jonesboro, Arkansas, quoted Richard Dennis, police chief of the town of Wynne, about 161km east of Little Rock near the Tennessee border, as saying "there is total destruction throughout the town", with dozens of people trapped.
Little Rock's Scott said property damage in the capital city was "extensive" although the full scale of devastation remained unclear.
"We're operating in red status, with all hands on deck," Metropolitan Emergency Medical Services agency spokesman Aaron Gilkey said.
Aerial footage posted by The Weather Channel showed a heavily damaged area of the city spanning several blocks with numerous homes missing roofs and walls, some of them collapsed, and overturned vehicles littering streets.
The turbulent weather came a week after a previous swarm of thunderstorms unleashed a deadly tornado that devastated the Mississippi town of Rolling Fork, destroying many of the community's 400 homes and killing 26 people.
Video shot on Friday from a window in a Baptist Health facility and verified by Reuters showed a towering, swirling black column of air, moisture and dust moving slowly through the landscape in the near distance.
Mayor Scott said on Twitter he had asked Governor Huckabee Sanders to mobilise National Guard troops to assist in the emergency response.
The twister struck as a blast of extreme spring weather swept much of the US, menacing the nation's midsection from Texas to the Great Lakes with thunderstorms and tornados.
The National Weather Service was tracking at least three dozen unconfirmed tornado reports in Arkansas, Tennessee, Illinois and Iowa.
Tens of millions of Americans across the Great Plains, Midwest, South and East were under warnings and advisories for various weather hazards on Friday evening and into the weekend, the NWS said.
Besides Arkansas, southern Missouri, western Kentucky and western Tennessee were deemed at greatest risk of severe thunderstorms capable of producing violent tornados, large hail and damaging winds, the weather service said.
