Three people were fatally shot and two were injured, including a 12-year-old girl, at an Indiana mall after a man with a rifle opened fire in a food court and an armed civilian shot and killed him, US police said.

The man entered the Greenwood Park Mall on Sunday evening with a rifle and several magazines of ammunition and began firing in the food court, Greenwood Police Department Chief Jim Ison said.

The three people who died were in addition to the man with the rifle. The identity of the gunman and a possible motive were not immediately known.

A 22-year-old from nearby Bartholomew County who was legally carrying a firearm at the mall shot and killed the gunman, Mr Ison said at a news conference.

“The real hero of the day is the citizen that was lawfully carrying a firearm in that food court and was able to stop the shooter almost as soon as he began,” he added.

The mass shooting was the latest to unnerve Americans in 2022. Schools, churches, supermarkets and a July Fourth parade in Highland Park, Illinois, have all become killing grounds in recent months.