A protester stands near a wall with a graffiti and police officers in Oakland, on Monday. (Associated Press)
The town of Ferguson erupted in violence as protesters shot at police and set cars and buildings ablaze Monday night after a grand jury chose not to indict a white officer who killed an unarmed black teen.
In the latest case to trigger debate on forceful police tactics against minorities and race relations in America, hopes and appeals -- including from President Barack Obama -- for a peaceful reaction to the decision evaporated quickly.
Many protesters took the ruling as a message that a black person's life was worth less than that of a white person.
Groups of youths roamed the streets, looting stores and spreading mayhem, as flames lit up the night sky in this suburb of St Louis, Missouri.
At least 12 buildings and two police cars were set on fire and destroyed.
But no one was killed or seriously hurt and police did not open fire at any point, said St. Louis County police chief Jon Belmar.
Twenty-nine demonstrators were arrested.
The grand jury concluded that officer Darren Wilson, who shot at 18-year-old Michael Brown 12 times, had acted in legitimate self defense after they got into an "altercation" as the officer investigated a robbery at a store, said St Louis County Prosecuting Attorney Robert McCulloch.
But a separate federal civil rights investigation into the Wilson incident and Ferguson policing in general will continue, US Attorney General Eric Holder said.
After the violence broke out in Ferguson, protests quickly spread to major US cities, including New York, Los Angeles, Chicago and Washington, but there were no reports of violence.
In Ferguson, a mainly black town with a mainly white police force, officers were stunned by a spasm of fury right after the hotly awaited verdict. It came after three months of deliberations by the grand jury following Brown's death in August.
Belmar said he had hoped the reaction "might not be too bad."
"But frankly, as soon as Mr. McCulloch announced the verdict, the officers started taking rocks and batteries," he told a press conference a few hours after midnight.
"I personally heard about 150 shots fired," he added. A highway patrol officer told him his men felt like "we were in a death funnel," Belmar said.
As the unrest continued into the night, Missouri Governor Jay Nixon called in additional National Guard forces to help restore order.
Brown's death in August had sparked weeks of sometimes violent protests. But Monday's episode was worse, Belmar said.
As McCulloch rounded off his summary of the grand jury's decision, Brown's mother burst into tears and a crowd began to chant: "Hey, hey, ho, ho! These killer cops have got to go."
Riot officers responded to protesters with teargas, batons and flash grenades, and running battles broke out, with armored cars moving slowly through the area.
Looters smashed their way into a mobile phone store opposite the police headquarters and ransacked it. An AFP journalist was hurt when he was hit in the face with a brick.
Pat Bailey, a retiree from St Louis in her 60s, said she had expected the decision. "I've lived long enough to know that African Americans are not considered human beings," she said.
- Obama appeals for calm -
Outside the White House in Washington, a crowd waved signs urging the government to "Stop racist police terror."
Obama made a rapidly-organized televised appearance to appeal for calm, echoing the sentiments of the dead teenager's family.
"Michael Brown's parents have lost more than anyone. We should be honoring their wishes," Obama said.
McCulloch told reporters the evidence presented to the jury had shown that Wilson had shot in a legitimate act of self-defense during a tussle that broke out as he was responding to a robbery.
He said the "altercation" had broken out as Wilson was sitting in his patrol car and Brown was at the window. Wilson testified to the jury that Brown leaned into the car and attacked him, grabbing his gun.
A picture taken after the incident and released by the prosecutor showed Wilson with a very slight bruise to his right cheek.
- Twelve shots -
"During the altercation, two shots were fired by Officer Wilson while still inside the vehicle," McCulloch said.
After these shots were fired, Wilson is said to have left the car to pursue Brown, who at some point turned on him. Ten shots were fired and the young man was killed, hit six times.
Some early witnesses had said in August that Brown had his hands up and was surrendering when he was killed. But McCulloch said the physical evidence and other witnesses contradicted this account.
In a statement, the Brown family said: "We are profoundly disappointed that the killer of our child will not face the consequence of his actions."
- Plea for non-violence -
Ferguson's African American community of 21,000 has been on edge for days, braced for further protests ahead of the ruling.
Residents complain of years of racial prejudice and heavy handed police tactics.
In the days leading up to the decision, Missouri's governor declared a state of emergency and called up the National Guard in readiness. The FBI has also deployed extra personnel.
The violence was to some extent reminiscent of riots that swept Los Angeles and other US cities in 1992 after white police officers who had been filmed beating a black man named Rodney King were acquitted of most charges against them.