NEW YORK - Police have clashed with protesters in Ferguson, a town in the US state of Missouri, after a grand jury on Monday night refused to charge a white policeman, Darren Wilson, over the death of unarmed black teenager Michael Brown, according to American media reports.

Announcing the decision, state prosecutor Robert McCulloch said the jury exhaustively examined evidence. "They determined that no probable cause exists to file any charge against Officer Wilson," McCulloch said.

The announcement was made late Monday night as crowds gathered outside the Ferguson Police Department, at McCulloch's offices in the county seat of Clayton and on West Flourisant Street, where Brown died.

Brown's family said they were "profoundly disappointed". Shots were fired, and cars and buildings burned.

Michael Brown, 18, was killed by Darren Wilson in Ferguson on 9 August. His death sparked weeks of demonstrations. Prosecutor McCulloch said all the evidence presented to the grand jury would be made public.

Policeman Wilson could have faced one of five charges ranging from first-degree murder to involuntary manslaughter. McCulloch said there was "no question" Wilson caused the death of Brown when he shot him Aug. 9.

The grand jury heard testimony from several witnesses who provided conflicting reports, McCulloch said, adding that the law provides for civilians and police alike to shoot upon another person in self-defence.

Less than an hour after the announcement that there would be no indictment, President Barack Obama echoed other officials' call for peaceful protests.

"We need to recognize that the situation in Ferguson speaks to broader challenges we face as a nation," he said.

"The fact is in too many parts of the nation a deep distrust exists between law enforcement and communities of color. Some of this is the result of the legacy of racial discrimination in this country."

Obama said he has instructed US Attorney General Eric Holder to work with communities and law enforcement in cities across the nation to build better relationships.

A spokesman for Brown's family told CNN that the teen's father, Michael Brown Senior, was "devastated" by the news that Wilson will face no charges told CNN.

"We are profoundly disappointed that the killer of our child will not face the consequence of his actions," the family said in a statement. "While we understand that many others share our pain, we ask that you channel your frustration in ways that will make a positive change. We need to work together to fix the system that allowed this to happen."

Police launched canisters of smoke after some protesters smashed the windows of a police cruiser. A St. Louis County Police car was also set on fire.

Law officers were heard telling the crowd to move because they were taking part in unlawful assembly. Lawyers for Wilson issued a statement saying the officer's "actions on Aug. 9 were in accordance with the laws and regulations that govern the procedures of an officer."

"Law enforcement personnel must frequently make split-second and difficult decisions. Officer Wilson followed his training and followed the law. We recognize that many people will want to second-guess the grand jury's decision. We would encourage anyone who wants to express an opinion do so in a respectful and peaceful manner," the statement continued.

Meanwhile, the American Civil Liberties Union issued a statement saying Brown's death "is part of an alarming national trend of officers using excessive force against people of colour, often during routine encounters."

Sources close to Wilson, who took the unusual step of testifying before the grand jury, have said the officer was defending himself in the shooting. They say Brown, 18, went for Wilson's gun and later charged at him.?

Witnesses who spoke publicly in the days and weeks after the shooting said they saw Brown raise his hands in apparent surrender before Wilson fatally shot him.

The tension over conflicting stories led to protests and property damage in Ferguson in the days and weeks that followed.

Law enforcement officials said they were bracing for unrest no matter the grand jury's decision. Protesters say they were planning a peaceful shutdown of the business district of Clayton.

Missouri Governor Jay Nixon declared a 30-day state of emergency last week and called in the National Guard to provide backup to local law enforcement in St. Louis County.

Beyond Missouri, communities across the United States reacted to the grand jury's decision.

In Chicago, hundreds of demonstrators marched on Lake Shore Drive, shouting, "Whose streets? Our streets." "We want freedom, freedom! All these dirty racist cops! We don't need 'em, need 'em! Back up, back up!" they chanted.

In South Los Angeles, dozens huddled around a speaker in a park for the news, many reacting with tears. Leisette Rodriguez of Long Beach said her first thoughts were of Brown's family: "My heart is hurting so much for them."