Residents sifted through piles of rubble Monday as they recovered from violent tornadoes that ripped through four midwestern US states, killing at least seven people and injuring dozens.

An unusually powerful fall storm spawned reports of 81 twisters in Illinois, Indiana, Kentucky and Ohio on Sunday along with powerful winds and heavy rain which soaked a dozen states.

Homes were smashed into rubble, cars and trucks were tossed into the air, trees were ripped out of the ground and downed power lines left hundreds of thousands of people in the dark.

In the hard-hit town of Washington, Illinois Michelle Cumrine came back from a trip to find that her house was completely gone.

"A lot of people have a pile of rubble still," Cumrine said in disbelief as she stared at the destruction. "I don't have anything. It's gone. I don't know where it went."

Illinois Governor Pat Quinn declared a state of emergency in seven counties where hundreds of homes and business were destroyed and six of the storm's fatalities were reported.

"As we pray for the families of those who have lost their lives and others who are injured, the state of Illinois will do everything necessary to help these communities recover," Quinn said in a statement.

Indiana Governor Mike Pence said he was thankful that despite the massive property damage and significant number of injuries "there has been no loss of life in the Hoosier state."

"We will help these families pick up the pieces and move on with their lives," he told reporters after touring some of the damage.

President Barack Obama was briefed about the storms and will receive regular updates, the White House said.

The fast moving storm weakened overnight but still caused damage as it marched east through New York and Philadelphia, the National Weather Service said.

The service predicted stormy conditions for much of the northeastern United States on Monday, including hail and isolated tornados, but said it would likely be over by the afternoon.

At least two victims were killed in the small town of New Minden, Illinois, Washington County Coroner Mark Styninger told AFP.

Joseph Hoy, 80, was found dead on his farm while his 78-year-old sister Frances was pronounced dead in hospital.

"It just happened so fast," said Styninger.

Some 55 people were treated at St. Francis hospital in Peoria, the biggest town in largely rural central Illinois. Of those, 16 were so badly injured they needed to be admitted, the hospital said.

The dangerous weather caused the National Football League to suspend a game in Chicago, asking fans and players to take cover in the stadium. The game resumed almost two hours later.

The town of Washington, Illinois was among the hardest-hit with entire blocks of homes flattened.

Tears welled up in the mayor's eyes as he struggled to describe the damage.

"Devastating. A war zone," Mayor Gary Manier told reporters. "I walked through one of the hardest hit areas and four streets of homes are gone. ... I couldn't tell what street I was on."

In Kokomo, Indiana the storm pushed a two story house off its foundation and into the middle of the street.

Michael Gardner, 21, had just come home from church with four friends when the storm hit. They rushed into the basement for shelter, with the last person having to jump down the stairs as the house started to move.

"It all caved in on us," Gardner told the Kokomo Tribune. "We were buried in rubble."

A Michigan man was killed when his car was crushed by a fallen tree Sunday night in rural Jackson county, MLive news reported.

The storm also grounded flights across the region.