Police cars have been vandalised and several gunshots have been heard on the streets of Ferguson after the announcement that a white police officer will not be indicted over the shooting death of an unarmed black 18-year-old.
About 15 minutes after St Louis County Prosecutor Bob McCulloch announced Officer Darren Wilson would not be indicted, county police used a bullhorn to tell crowds outside the Ferguson Police Department to disperse, saying it had become an unlawful assembly.
Protesters hugged a barricade and taunted police, sometimes with expletives. Some chanted “murderer.” Gunshots were heard down the street and somebody threw a water bottle that bounced off a police shield.
Some in the crowd reportedly tried to stop others from taking part in vandalism and other violent reactions.
The trouble was happening as President Barack Obama said he joined with Michael Brown’s family in urging peaceful protests after a grand jury decided not to indict the Ferguson police officer who shot and killed the teenager.
Mr Obama made the comments moments after official word of the grand jury’s decision.
The president said first and foremost the nation is built on the rule of law. He said despite anger and intense disagreement on either side, Americans need to accept the decision that the grand jury made.
The US Justice Department is conducting an investigation into possible civil rights violations that could result in federal charges.
It has also launched a broad probe into the Ferguson Police Department, looking for patterns of discrimination.
The death of Mr Brown on August 9 sparked weeks of violent protests, and led Missouri Governor Jay Nixon to briefly summon the National Guard.
Mr McCulloch announced the decision this morning. A grand jury of nine whites and three blacks had been meeting weekly since August 20 to consider evidence.
At least nine votes would have been required to indict Mr Wilson.
The decision of the grand jury, which met in secret, as is standard for such proceedings, had prompted an angry response from demonstrators.
Mr Brown’s killing reignited a debate over how police treat young African-American men four decades after the civil rights movement of the 1960s and focused attention on long-simmering racial tensions in Ferguson and around the US.
Mr McCulloch stressed the grand jurors were “the only people who heard every witness ... and every piece of evidence”.
He said many witness presented conflicting statements that ultimately were inconsistent with the physical evidence.
“These grand jurors poured their hearts and soul into this process,” he said.
As he was reading his statement, a crowd gathered around a car from which it was being broadcast on a stereo.
When the decision was announced, Mr Brown’s mother, Lesley McSpadden, who was sitting on top of the car, burst into tears and began screaming before being whisked away by supporters.
The crowd erupted in anger, converging on the barricade where police in riot gear were standing. They pushed down the barricade and began pelting police with items, including a bullhorn. Police stood their ground.
The grand jury had been considering charges against Mr Wilson, who fatally shot Mr Brown after a confrontation.
The shooting inflamed tensions in the predominantly black St Louis suburb that is patrolled by an overwhelmingly white police force.
Rioting occurred the following night, protests erupted for weeks and police responded with armoured vehicles and tear gas.
The tensions evoked other racially charged cases, including the riots that rocked Los Angeles in 1992 after the acquittal of white police officers in the videotaped beating of black motorist Rodney King.
More recently, peaceful protests followed last year’s not-guilty verdict in the Florida killing of unarmed black teenager Trayvon Martin by George Zimmerman, who was not a police officer but co-ordinated the local neighbourhood watch.
Mr Nixon travelled to St Louis from the state Capitol and held a news conference ahead of the announcement, asking for “peace, respect and restraint”.
The authorities quickly stepped up security around the courthouse where the decision was announced. Barricades were erected, and more than 20 Missouri state troopers were seen silently assembling with rifles, batons, riot shields and other equipment.
Some nearby businesses boarded up their windows, just as many shops have already done near the site of Mr Brown’s death in Ferguson.
Hours before the announcement, dozens of people gathered in the car park across the street from the Ferguson Police Department. Many chanted slogans such as: “No justice, no peace, no racist police.”