A tornado that ripped through the midwestern US state of Iowa killed five people and left dozens injured, officials said, with homes smashed to pieces and cars thrown through the air.

Residents surveyed the wreckage of flattened buildings and uprooted trees after the storm left a path of destruction across the town of Greenfield on Tuesday.

"Four fatalities and at least 35 injuries were the result of the tornado that impacted the Greenfield, Adair County area," the Iowa State Patrol said Wednesday, adding that the number of injured could still rise.

The local hospital was damaged and some patients were moved to other facilities, while airlift flights were also undertaken after the storm slammed the town of 2,000 residents 70 kilometres from state capital Des Moines.

More than 100 emergency workers combed through the debris, said Iowa Governor Kim Reynolds, while local officials reported at least one other person was also killed in nearby Adams County.

Tornado reports in the United States have been far above average in recent weeks, according to CNN, with more than 800 tornadoes this year making it one of the most active on record. (AFP)