Police have released few details about the incident, only confirming an officer was involved in the shooting death of Mike Brown, and that the officer was placed on administrative leave.
Witnesses said they observed Brown being shot multiple times while his hands were in the air, KMOV-TV, St. Louis, reported.
Dorian Johnson said he was walking with Brown when an officer confronted the pair and drew his weapon.
"He (the officer) shot again and once my friend felt that shot, he turned around and put his hands in the air," Johnson said. "He started to get down and the officer still approached with his weapon drawn and fired several more shots."
Desuirea Harris, Brown's grandmother, said her grandson didn't live in the area and had come to visit her.
Police urged the community to remain calm after a crowd of protesters set a dumpster on fire near where the incident occurred.
Police said they were investigating the death.