Washington, Illinois in this photo courtesy of Anthony Khoury. Photo: Reuters/Anthony Khoury

The city of Washington, Illinois, was hit hard by what the National Weather Service called a "large and extremely dangerous" tornado.

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Thirty-one people injured by the storm that hit Washington were being treated at St Francis Medical Centre, one of the main hospitals in nearby Peoria, said hospital spokeswoman Amy Paul. Eight had traumatic injuries.

Two people were killed in Washington County, Illinois, about 320 kilometres south of Peoria, said Illinois Emergency Management Agency spokeswoman Patti Thompson. The agency estimated that 70 homes were destroyed across the state.

Residents search through debris following the likely tornado touch down in Gifford, Illinois. Photo: AP

Stephen Wilson, a spokesman for Peoria's Proctor Hospital, said six or seven patients were being treated with minorinjuries. "Mostly cuts, bruises, some broken bones," he said.

Photos from Washington, Illinois, showed buildings reduced to rubble and homes torn in half in the city of 15,000 people about 230 kilometres south-west of Chicago.

"We have reports of homes being flattened, roofs being torn off," Sara Sparkman, a spokeswoman for the health department of Tazewell County, Illinois, where Washington is located, said. "We have actual whole neighbourhoods being demolished by the storm."

An active tornado is seen through a window as it touches down in Washington, Illinois, in this still image captured from a video courtesy of Anthony Khoury. Photo: Reuters/Anthony Khoury

Ms Sparkman said the storm also had caused damage in Washington and Pekin, south of Peoria.

Many of the injuries appeared to have been caused by collapsing structures.

"Things falling on