HARRISBURG, Illinois — A massive winter storm unleashed a string of tornadoes that cut a swath of destruction across the US midwest, killing at least nine people and threatening scores more as it pushed eastward Wednesday.

The town of Harrisburg, Illinois was ripped apart by a deadly twister that stayed on the ground for miles, striking while most were still sleeping at around 4:30 am (10:30 GMT.)

Homes were smashed to bits, cars were tossed into lakes, huge trees were torn from ground, a strip mall was ripped to rubble and a wall was torn off the local hospital.

At least six people were killed and more than 100 injured in this southern Illinois town of 9,000.

The monster twister packed winds up to 170 miles (270 kilometers) per hour and damaged or destroyed up to 300 homes and 25 businesses.

"A lot of the houses are unreal, it's like a war zone," fire chief Bill Summers told reporters.

Rescue crews were digging through the rubble to search for survivors, but Summers said that by late afternoon all those who had been reported missing had been accounted for.

Harrisburg mayor Eric Gregg called the destruction and loss of life "devastating" and vowed to protect and care for those who were hurt and displaced.

"Dealing with a tornado like this is heartbreaking," Gregg said at a press conference.

"We will build this city. We will make this city strong. This will not stop us. It will make us stronger."

Angela Capps was among those who sought shelter at the First Baptist Church.

A neighbor called her to warn her of the oncoming twister, so Capps and her children were able to take cover and escape injury.

"Even right now we're emotionally fine," Capps said as she sat with her neighbor while their children played nearby.

"We haven't cried yet, for the kids. I'm sure we'll go in the bathroom eventually and bawl our eyes out."

The National Weather Service has received 22 reports of tornadoes in six states since the storm began Tuesday, battering Nebraska and Kansas, then moving eastward to Missouri, Illinois, Indiana and Kentucky.

Severe thunderstorms were expected to continue to pound Alabama, Georgia, Kentucky, Mississippi, North Carolina and Tennessee Wednesday before moving to the eastern seaboard.

"It's a very large storm," said Corey Mead, lead forecaster for the weather service's storm prediction center.

"There have been a number of tornado reports in addition to damaging winds and hail. We're expecting that threat to continue into today and tonight."

The governor of Illinois issued a state of emergency and went to Harrisburg to tour the damage.

"My heart goes out to the victims of this devastating storm, and I would like to thank the many people who have stepped up and volunteered to aid their neighbors," Governor Pat Quinn said.

"I have met with local community leaders and first responders, and they know the state of Illinois is here to help as they recover from this disaster."

Missouri's governor also declared a state of emergency after at least three people were killed by tornadoes which ripped across the southern portion of the state, causing extensive damage in the towns of Branson, Buffalo, Cassville, Lebanon and Oak Ridge.

The deadly storm marks an early start to tornado season in a region still recovering from record-breaking severe weather outbreaks.

Some 545 people were killed by tornadoes in 2011, which was the deadliest tornado season since 1936 and the third worst on record, according to the national weather service.

Two bad days accounted for nearly all the deaths: an outbreak of dozens of tornadoes that killed 314 people in five states on April 27 and a nearly mile-wide twister that struck Joplin, Missouri on May 22, killing 159 people.

Some 95 tornadoes struck the US in January, causing just two fatalities, the weather service said.