A fast-moving storm system triggered multiple tornadoes that killed at least six people and flattened large parts of a town in Illinois as it moved across the US Midwest.

A US National Weather Service survey team confirmed preliminary EF-4 tornado damage in Washington County in southern Illinois, with winds of 267-322km/h.

A total of 80 tornado reports were received by the Storm Prediction Center in Oklahoma, along with 358 reports of damaging winds and 40 reports of large hail.

The storm moved dangerously fast, tracking eastward at 97km/h and the bulk of the tornado damage from the storm occurred over a period of about five hours.

The storm also forced the Chicago Bears football team to halt their match against the Baltimore Ravens and NFL fans at Soldier Field to seek shelter as clouds rolled in.

Chicago's two major airports briefly stopped traffic while the metropolitan area was under a tornado watch.

The town of Washington, 233km southwest of Chicago, was hit especially hard by the tornadoes, which had moved through Indiana and Kentucky as well as Illinois and a small corner of Ohio.

"It's a sad day in Washington. The devastation is just unbelievable," said Washington Mayor Gary Manier.

"I can't imagine people walked away from these places. Some people were sitting in their living rooms. They stayed but their house left," he later added.

Mr Manier said hundreds of homes had been destroyed in the town of 15,000 people.

The state Emergency Management Agency said one person was killed in Washington.

Thirty-one people injured by the storm were being treated at St Francis Medical Center, one of the main hospitals in nearby Peoria. Eight had traumatic injuries.

Two people were killed in Washington County about 320km south of Peoria.

Three people were killed in Massac County, Illinois, on the Kentucky border where a twister devastated several neighbourhoods, emergency officials said.

Illinois State Police spokeswoman Monique Bond said officials believe some people may be trapped in their basements under debris.

A dusk-to-dawn curfew was imposed in the town of Washington, where State Police spokesman Dustin Pierce said there had been looting amid gas leaks and downed power lines.

The American Red Cross worked with emergency management officials to set up shelters and provide assistance to displaced residents.

Rescue workers searched for more people who might have been caught in the storm's path.

The Washington tornado came out of a fast-moving storm system that originally headed toward Chicago as it threatened a large swath of the Midwest with dangerous winds, thunderstorms, and hail, US weather officials said.