The fatal shooting of a black teenager sent hundreds of angry residents out of their apartments in a predominantly black Missouri city 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 black teen was identified as Michael Brown.

The teenager's grandmother, Desiree Harris, saw the 18-year-old 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 to visit her that afternoon but discovered him dead after she heard the commotion outside the apartment complex in Ferguson, a northern 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."

"My grandson never even got into a fight," she said. "He was just looking forward to getting on with his life. He was on his way."

Brown's mother, Lesley McSpadden, told an acquaintance the shooting was "wrong and it was coldhearted", 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 the St. Louis County Police Department, which is investigating the shooting at the request of the local department, confirmed that a Ferguson police officer shot the man. The spokesman didn't give the reason for the shooting.

John Gaskin, a member of the St. Louis County NAACP, the local chapter of the civil rights group, said the FBI should get involved "to protect the integrity of the investigation".

He alluded to the 2012 racially charged shooting of Trayvon Martin, a 17-year-old high school student, by a Florida neighborhood watch organizer who was subsequently acquitted of murder charges, and to the death of a New York man from a police chokehold after he was confronted for selling individual cigarettes on the street.

Gaskin said officials in the organization spoke with St. Louis County Police Chief Jon Belmar, who told them the teenager had been shot twice.

At the height of the post-shooting tensions, police at the scene called for about 60 other police units to respond to the area in Ferguson, a city of about 21,000 residents, about two-thirds of whom are black.