Three people were killed at a mall in Greenwood, Ind., in a mass shooting that ended when another armed individual fatally shot the gunman, city authorities said.

Two additional people were hospitalized in the shooting, which began when a man with a rifle and several magazines of ammunition entered the food court and started firing, Chief Jim Ison of the Greenwood Police Department said. The authorities did not indicate a motive for the shooting and did not identify the gunman.

Mayor Mark Myers said late Sunday that the public faced no further threat and that the Greenwood Police Department was in control of the scene. He asked the public to stay away from the area.

“I’ve been a police officer most of my life,” he said in an interview. “Still, this is incredibly shocking, to not only me but our entire community.”

Mr. Ison said at a news conference on Sunday that the local emergency call center began to receive calls about the shooting around 6 p.m. He said the threat ended when an armed passer-by, who had a handgun, stopped the gunman. “It appears that a good Samaritan that was armed observed the shooting in progress and shot the shooter.”

He added that investigators and other personnel would not process the crime scene at the mall until a state bomb squad could determine whether a “suspicious” backpack that was left in a mall bathroom was dangerous.

The police said on Facebook that they were seeking witnesses to the shooting, which took place about 15 miles south of Indianapolis.

The Indianapolis Metropolitan Police Department said on Twitter that it was helping the local authorities and urged people to avoid the area.