At least four people were killed and more than 40 were injured when a stage collapsed during a severe storm at a state fair in the midwestern U.S. of Indiana.

The deadly incident occurred at the Indianapolis State Fair just before the country music group Sugarland was about to mount the stage to perform. No one was on the stage when it came down.

Officials says the rigging supporting the stage collapsed without warning though an announcer had alerted the concert goers that severe weather was possible.

Sugarland, in a Twitter message, said the group's members were all right. “We are praying for our fans,” the message said, “and for the people of Indianapolis.”

State fairs are widely popular across the United States, attracting tens of thousands of followers over several days each year, usually in late summer.

The fairs showcase agriculture and livestock, music, rides, talent demonstrations, and food.