Shots were fired during a march marking one year since a white police officer killed unarmed black teenager Michael Brown.
About six shots were heard as around 300 people made their way to a church on the outskirts of Ferguson, USA.
Police said is was initially unclear who fired the shots or if anyone was injured.
The march was stopped while police and ambulance crews rushed to an area behind a church where the shots were thought to have come from.
Hundreds of people have gathered in Ferguson, USA, to mark one year since unarmed black teenager Michael Brown was shot dead by a white police officer.
A four-and-a-half minute silence was held at the spot where he was killed to represent the roughly four-and-a-half hours the 18 year old's body lay in the street after being shot.
The crowd, which included his father Michael Brown Snr, then took part in a silent march in memory of the teen and others killed by police.
At the memorial, Brown's father wore a T-shirt bearing his son's image and the slogan "Chosen for Change." Others held "Black Lives Matter" banners and signs calling for justice for those killed by police.
Brown's death sparked months of protests in America, including incidents of rioting and arson.
The family of Michael Brown, the unarmed black teenager shot dead by US police last summer, have filed a wrongful death civil lawsuit against the city of Ferguson, Missouri.
Brown was fatally shot by former Ferguson police officer Darren Wilson in August.
In November, a grand jury elected not to file charges against Wilson. A federal investigation later determined that Wilson should not be charged.
The shooting last August sparked a wave of angry demonstrations and unrest over police violence, particularly against minorities in Ferguson and around the US.
The police officer who shot and killed an unarmed black teenager in Ferguson, Missouri, did not get a severance deal when he resigned, the mayor has confirmed.
Darren Wilson handed in his notice after days of protests in the town following a grand jury's decision not to indict him for the shooting, saying he feared for his own safety and that of his fellow officers.
Ferguson Mayor James Knowles confirmed Wilson would get "no severance or extension of benefits" after his resignation.
The mayor of Ferguson, the St. Louis suburb torn apart by clashes over the shooting of unarmed black teenager Michael Brown, said the community must move on.
His remarks came after the resignation of officer Darren Wilson, who shot Mr Brown, announced his resignation.
Mayor James Knowles said he had not asked for Wilson's resignation, and even though the officer expressed an interest "in a future here," Mr Knowles said he wanted the city to turn a page.
"I think it is best that we continue to move on as a community," he said.
The police officer who shot dead unarmed black teenager Michael Brown has resigned from his position.
But Darren Wilson's departure is unlikely to put an end to the frustrations and disquiet many in the communtiy feel over the incident.
ITV News Correspondent Sascha Williams reports.
Over a hundred protesters in Ferguson, angry at the decision not to indict Darren Wilson for killing unarmed black teenager Michael Brown, have started a week-long peace march to Jefferson City.
The 135-mile march is being organised by the National Association for the Advancement of Coloured People in an attempt to bring peaceful visibility on the need for reform in the justice system.
NAACP president Cornell William Brooks told the St Louis Post:
What we’re endeavoring to do is seek justice for a grieving family and systemic change and reforms at the municipal, state and federal levels.
Participants will walk more than 20 miles during the day and start at churches at night.
The police officer Darren Wilson who killed Michael Brown has resigned from the Ferguson Police Department, his attorney said, according to Associated Press.
The news agency reported the decision, which comes nearly four months after the fatal confrontation with the black 18-year-old that fueled protests in the St. Louis suburb and across the nation.
Darren Wilson, 28, has been on administrative leave since the shooting on Aug. 9. His resignation was announced Saturday by one of his attorneys, Neil Bruntrager. AP reported Mr Bruntrager as saying the resignation is effective immediately.
Ferguson officer Darren Wilson resigns in wake of fatal shooting of Michael Brown, Associated Press is reporting.
BREAKING: Attorney: Ferguson officer Darren Wilson resigns in wake of fatal shooting of Michael Brown.
Fifteen people were arrested overnight in Ferguson after taking part in protests against a decision not to indict the white police officer who killed an unarmed black teenager.
Tensions escalated after police said protesters began illegally blocking an avenue.
A group of around 100 protesters had marched down the avenue towards the city's police and fire departments chanting, blocking traffic and stopping in front of businesses. One protester said:
I served my country. I spent four years in the Army, and I feel like that's not what I served my country for. I served my country for justice for everyone. Not because of what colour, what age, what gender or anything.