There are many police cars on site outside the King Soopers store. TV pictures from the place showed a man in only his underwear being taken away by the police. He had blood running down his leg and was handcuffed.
A man who was in the store told the TV station ABC News that he heard a great bang, then one more. When it slammed for the third time, everyone started running, the man said.
Witnesses have told the Associated Press that they saw several people lying on the ground in the parking lot outside the store and also inside the store, but it has not been confirmed that anyone is dead or injured.
TV pictures from the place show that some of the windows in the shop are broken. Photos show a number of police vehicles and many police officers outside the building. At least three helicopters have landed on the roof of the building where the supermarket is located.