Violence erupted again on Tuesday night in Missouri as armed police clashed with protesters in angry demonstrations over the shooting of an unarmed black teenager.

The death of 18-year-old Michael Brown on Saturday has sparked days of unrest in the city of St Louis, despite calls for calm by Barack Obama and community leaders.

Around 250 demonstrators were stopped by police from entering the road where Mr Brown had been on the way to visit his grandmother in the suburb of Ferguson.

A wall of armed police formed a barricade across Florrisant Street, where protests had flared up the previous nights, leading to looting and vandalism by small groups on Sunday.

Officers ordered protesters to “get out of the road or face arrest” before firing teargas, rubber bullets and baton rounds into the crowd.

Photos showed SWAT teams in military-style uniforms pointing guns at protesters and some individuals were seen hurling missiles and teargas cannisters back at the police line.

Some raised their arms above their heads and repeated what has become a defining slogan: "Hands up, don't shoot."

In pictures: Michael Brown shooting Show all 32 1 /32 In pictures: Michael Brown shooting In pictures: Michael Brown shooting Michael Brown shooting Riot police stand guard as demonstrators protest the shooting death of teenager Michael Brown in Ferguson In pictures: Michael Brown shooting Michael Brown shooting Police stand watch as demonstrators protest the shooting death of teenager Michael Brown in Ferguson In pictures: Michael Brown shooting Michael Brown shooting A police officer patrols a business district in Ferguson In pictures: Michael Brown shooting Michael Brown shooting Police surround and detain two people in a car in Ferguson In pictures: Michael Brown shooting Michael Brown shooting A protester throws back a smoke bomb while clashing with police in Ferguson In pictures: Michael Brown shooting Michael Brown shooting A protester is engulfed in smoke as he throws back a smoke bomb while clashing with police in Ferguson In pictures: Michael Brown shooting Michael Brown shooting A demonstrator, protesting the shooting death of teenager Michael Brown, stands his ground as police fire tear gas in Ferguson In pictures: Michael Brown shooting Michael Brown shooting A demonstrator throws back a tear gas container after tactical officers worked to break up a group of bystanders on Chambers Road and West Florissant in St. Louis In pictures: Michael Brown shooting Michael Brown shooting A member of the St. Louis County Police Department points his weapon in the direction of a group of protesters in Ferguson In pictures: Michael Brown shooting Michael Brown shooting Michael Brown’s parents, Michael Brown Sr, left, and Lesley McSpadden, right, stand next to the Rev Al Sharpton in St Louis AP In pictures: Michael Brown shooting Michael Brown shooting Demonstrators protest the killing of teenager Michael Brown outside Greater St. Marks Family Church while Browns family along with civil rights leader Rev. Al Sharpton and a capacity crowd of guests met inside to discuss the killing in St Louis, Missouri In pictures: Michael Brown shooting Michael Brown shooting Demonstrators protest the killing of teenager Michael Brown in Ferguson In pictures: Michael Brown shooting Michael Brown shooting Police take up position to control demonstrators who were protesting the killing of teenager Michael Brown in Ferguson, Missouri In pictures: Michael Brown shooting Michael Brown shooting Police detain a man in Ferguson, Missouri In pictures: Michael Brown shooting Michael Brown shooting Demonstrators march in the street while protesting the shooting death of black teenager Michael Brown in Ferguson, Missouri In pictures: Michael Brown shooting Michael Brown shooting Police officers keep watch while demonstrators protest the death of black teenager Michael Brown in Ferguson, Missouri In pictures: Michael Brown shooting Michael Brown shooting Demonstrators protest the killing of teenager Michael Brown in Clayton, Missouri In pictures: Michael Brown shooting Michael Brown shooting Anthony Shahid leads a peaceful protest over the killing of teenager Michael Brown in Clayton, Missouri In pictures: Michael Brown shooting Michael Brown shooting Lesley McSpadden (L), the mother of slain teenager Michael Brown joins a capacity crowd of guests at Greater St. Marks Family Church to discuss the killing of her son and the civil unrest resulting from his death in St Louis, Missouri In pictures: Michael Brown shooting Michael Brown shooting Lesley McSpadden, the mother of 18-year-old Michael Brown, wipes away tears as Brown's father, Michael Brown Sr., holds up a family picture of himself, his son, top left, and a young child during a news conference in Jennings In pictures: Michael Brown shooting Michael Brown shooting Police with dogs in St Louis after vandalism started St Louis Post-Dispatch/AP In pictures: Michael Brown shooting Michael Brown shooting A man leaving a looted shop in St Louis following a vigil for Michael Brown on Sunday St Louis Post-Dispatch/AP In pictures: Michael Brown shooting Michael Brown shooting Protesters bang on the side of a police car Sunday evening, St Louis Post-Dispatch/AP In pictures: Michael Brown shooting Michael Brown shooting Meghan O'Donnell, 29, from St Louis, prays at the spot where Michael Brown was killed on Sunday evening St Louis Post-Dispatch/AP In pictures: Michael Brown shooting Michael Brown shooting A large crowd gathers at the candlelight vigil on Sunday evening St Louis Post-Dispatch/AP In pictures: Michael Brown shooting Michael Brown shooting Protesters raise their hands in the 'don't shoot me' stance after being approached by police officers on Sunday St Louis Post-Dispatch/AP In pictures: Michael Brown shooting Michael Brown shooting Lesley McSpadden, center, drops rose petals on the blood stains from her son AP Photo/St. Louis Post-Dispatch, Huy Mach In pictures: Michael Brown shooting Michael Brown shooting Lesley McSpadden, left, is comforted by her husband, Louis Head, after her son, was shot AP Photo/St. Louis Post-Dispatch, Huy Mach In pictures: Michael Brown shooting Michael Brown shooting Louis Head, stepfather to Michael Brown, holds a sign AP Photo/St. Louis Post-Dispatch, Huy Mach In pictures: Michael Brown shooting Michael Brown shooting Ferguson police officers try to calm down a crowd near the scene of Michael Brown's death AP Photo/St. Louis Post-Dispatch, Huy Mach In pictures: Michael Brown shooting Michael Brown shooting A crowd stages a protest AP Photo/St. Louis Post-Dispatch, David Carson In pictures: Michael Brown shooting Michael Brown shooting Police officers stand near a crowd that is gathering AP Photo/St. Louis Post-Dispatch, Huy Mach

As the crowds were dispersed shortly after midnight, another man was shot close to the scene of Mr Brown’s death.

Police said teams had been responding to reports of shots being fired and men armed with guns wearing ski masks.

He was shot while allegedly pointing a handgun at an officer, police said, and was in a critical condition in hospital.

President Obama promised a full investigation by the US Department of Justice into Mr Brown's death and the FBI has also stepped in.

"I know the events of the past few days have prompted strong passions," he said.

"I urge everyone in Ferguson, Missouri, and across the country, to remember this young man through reflection and understanding."

Friends and family of Brown held a peaceful church vigil on Tuesday night, after his father pleaded for an end to the violence. Standing with supporters, including the Reverend Al Sharpton, Michael Brown Sr. said he wanted justice for his son but wanted it "the right way."

"I need all of us to come together and do this right, the right way," he said, wearing a T-shirt showing his son's baby picture. "No violence."

Police officers keep watch while demonstrators (not pictured) protest the death of black teenager Michael Brown in Ferguson, Missouri (Reuters)

At another church gathering with dozens of clergy members and officials, the Governor of Missouri Jay Nixon urged calm “in the face of crisis".

“We stand together tonight, reeling from what feels like an old wound torn open afresh,” he said.

“A wound that hadn't quite healed right in the first place, and now the pain is just as searing as when the injury first occurred.”

Eyewitness accounts have contradicted the police department's account of events, which said Mr Brown was shot after a struggle for an officer's gun.

Dorian Johnson, 22, said he had been walking with his friend in the middle of the street when a police officer in a car reportedly told them to “get the f*** on the sidewalk”.

A struggle near the officer’s car followed, with Mr Johnson reporting that Mr Brown was shot at close range.

After being shot in the back as he tried to run away, he said his friend turned around with his hands up and said “I don’t have a gun, stop shooting!” but the officer reportedly shot him several more times.

Mr Johnson's version of events has been corroborated by several other eyewitness accounts, although police from Ferguson maintain that the teenager was killed following a struggle for the officer’s gun.

There is no security or police video footage of the incident, according to police.

Mr Brown's death has exposed deep racial and economic fault lines in the community.

Out of 53 officers in the Ferguson - a working class, mostly black suburb - only three are black and officials said the city has had trouble recruiting and retaining black officers.

Protests in St Louis after Michael Brown shooting

The identity of the officer involved, who witnesses said was white, has not been revealed and is currently on paid leave for the investigation.

Ferguson police said they initially planned to release the name of the officer but decided to withhold if after officers received death threats.