Unrest has broken out in Salt Lake City after a police officer reportedly shot a 16-year-old boy.

Angry crowds gathered at the scene in the Rio Grande district on Saturday night, throwing bottles and rocks at police officers.

A number of people were arrested as officers closed off nearby streets.

Selam Mohammad said his friend was holding a broomstick when officers ran up and shot him.

"The police said drop it once, then shot him four times," he said.

"The police ran on foot and pulled their guns out already.

"As soon as we was running he was already grabbing for his gun.

"Like not even trying to Taser him or anything like that. He said drop it - boom, boom - like four times."

He said his friend was shot in the chest and stomach, and was taken to hospital. His condition is not known.

Police confirmed shots were fired, but did not say who fired them.

Detective Greg Wilking, from Salt Lake City Police Department, said: "Our officers were responding to a situation down in front of the shelter here.

"While they were on scene, there were shots fired and officers called for more assistance.

"Several people were agitated in the crowd.

"Our officers started arriving on scene and encountered a lot of hostile people upset about what had taken place, and we began clearing the area."