CHICAGO - A fierce tornado blasted through Little Rock, Arkansas, and neighbouring towns on Friday, killing at least two people and injuring dozens as it sheared roofs and walls from many buildings, flipped over vehicles and downed trees and power lines, officials said.

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, in the mid-afternoon.

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, and we are not aware of any fatalities in Little Rock,” Mayor Frank Scott Jr said on Twitter.

Separately, Baptist Health Medical Centre 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. 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 Mr Richard Dennis, police chief of the town of Wynne, as saying “there is total destruction throughout the town”, and that dozens of people had been trapped in the storm. Wynne is located about 160km east of Little Rock near the Tennessee border.

KAIT also quoted a coroner as saying no fatalities were reported as at 6pm central time (7am on Saturday, Singapore time).

“We’re operating in red status, with all hands on deck,” said Mr Aaron Gilkey, spokesman for the Metropolitan Emergency Medical Services agency.

Aerial footage posted by The Weather Channel showed a heavily damaged area of Little Rock spanning several blocks, with numerous homes missing roofs and walls, some of them collapsed, and overturned vehicles littering streets.

KATV posted an image of a heavily damaged high school in the town of Wynne.

Close call in nail salon

Video footage shot on Friday from a window in a Baptist Health facility in Little Rock and verified by Reuters showed a towering, swirling black column of air, moisture and dust ploughing slowly through the landscape in the near distance.

One woman recounted in a live interview aired by KATV that she was visiting a salon to have her nails done when she looked out the window and saw leaves swirling moments before the building’s roof was torn off.

She and others in the shop took cover in a back room as the twister struck, and emerged to find the ceiling gone, said the woman, who seemed unhurt.

Little Rock’s Mayor Scott said on Twitter that he had asked Arkansas Governor Sarah Huckabee Sanders to mobilise National Guard troops to assist in the emergency response.

Ms Sanders signed an executive order to immediately authorise US$250,000 (S$330,000) from the state disaster response and recovery fund to be used at the discretion of the director of the state Division of Emergency Management, a local reporter tweeted.

The twister struck as a blast of extreme spring weather swept through much of the United States, menacing the nation’s mid-section, from Texas to the Great Lakes, with thunderstorms and tornados.

The National Weather Service is 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 afternoon and evening and into the weekend, the National Weather Service 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.

The northern, colder edge of the storm system, stretching from the High Plains to the upper Great Lakes, was expected to bring heavy snow, combining with winds gusting up to 80kmh to create blizzard conditions.

Somewhere in the middle, arching across parts of several states, was a swathe of the northern Midwest expected to be besieged by intense ice storms, with freezing rain wreaking havoc on roads and power lines.

This round of turbulent weather comes a week after 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. REUTERS