The shooting happened about 8:15 PM near downtown, the Salt Lake Tribune reported.
Selam Mohammad told the paper that a police officer shot a 16-year-old boy who was his friend.
In a tweet late last night, Salt Lake City police said that officers were responding to an unrelated call in area when they were told of assault in progress. The officers "tried to engage altercation," the tweet says.
Detective Greg Wilking told the Tribune that "shots were fired," but not how many or whether an officer fired them. Later yesterday, Salt Lake City police told the newspaper that one officer, and possibly a second one, were involved in the shooting.
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"They told him to put it down, once," Mohammad said, and "started shooting him as soon as he turned around."
The teenager was hit in the chest and stomach, Mohammad said. The victim was taken to a hospital, it reported.
City police were helped by officers from three other departments as onlookers threw rocks at officers and yelled obscenities, the paper said. Police have closed a light rail stop in the neighbourhood.
There were "a lot of hostile people upset about what had taken place," Wilking told the paper.
At 8:40 PM, a line of officers moved protesters down a sidewalk, the newspaper reported.
There are a number of homeless shelters in the neighbourhood, and business owners have long complained about the homeless population and drug dealing, the newspaper said.