The shooting of a black teenager sent hundreds of angry residents on to the streets of this predominantly black are in the US state of Missouri in a confrontation with police that lasted several hours.
They shouted obscenities and some threats, such as "kill the police", but there were no reports of additional injuries.
The teenager's grandmother, Desiree Harris, saw the recent high school graduate running near her home on Tuesday afternoon when she passed him in her car. Minutes later, she found his body on the street, fatally shot by a police officer.
Harris said she was expecting her grandson, Michael Brown, 18, to visit her that afternoon and discovered him dead after she heard the commotion outside the apartment complex in Ferguson, a suburb of St Louis.
"He was running this way," she said. "When I got up there, my grandson was lying on the pavement. I asked the police what happened. They didn't tell me nothing."
Brown's mother, Lesley McSpadden, told an acquaintance the shooting was "wrong and it was cold-hearted", the St Louis Post-Dispatch reported. According to the newspaper, Brown's stepfather, Louis Head, held a sign that read: "Ferguson police just executed my unarmed son!!!"
A spokesman with St Louis County Police Department, which is investigating the shooting at the request of the Ferguson police, confirmed a Ferguson police officer shot the man. The spokesman did not give the reason for the shooting.
John Gaskin, a member of the St Louis County NAACP civil rights group, said the FBI should be involved "to protect the integrity of the investigation".
He alluded to the 2012 racially charged shooting of a high school student by a Florida neighbourhood watch organiser who was subsequently acquitted of murder charges, as well as the death of a New York man from a police choke hold after he was confronted for selling individual cigarettes on the street.
"With the recent events of a young man killed by the police in New York City and with Trayvon Martin and with all the other African-American young men that have been killed by police officers ... this is a dire concern to the NAACP, especially our local organisation," Gaskin said.
He said officials in the organisation spoke with St Louis police chief Jon Belmar, who told them the teenager had been shot twice.
By early Saturday night, dozens of police cars remained parked near the shooting scene as mourners left candles, rose petals, a large stuffed animal and other remembrances at a makeshift memorial in the middle of the street.
At the height of the tensions, police called for about 60 other police units to respond to the area in the city of about 21,000 residents, about two-thirds of whom are black.
Ferguson police chief Thomas Jackson said that the officer involved has been placed on leave.
"We are hoping for calm and for people to give us a chance to conduct a thorough investigation," Jackson said.