Washington: Police shot down a young man after he opened fire at them in the US state of Missouri during protests to mark the first death anniversary of African-American teenager Michael Brown who was killed by a white police officer last year, media reports said on Monday.
St. Louis county Police Chief Jon Belmar said the man was in a critical and unstable condition, and undergoing surgery at a hospital in Ferguson, USA Today reported.
A St. Louis county officer was involved in a shooting after coming under heavy gunfire, said St. Louis County police on its official Twitter account.
Earlier, Belmar said the shooting occurred after undercover detectives monitored an individual in the crowd who they believed was armed and had three or four possible armed acquaintances.
A shootout also broke out between two groups and the suspect ran away. He was then spotted by police detectives in an unmarked vehicle, which began driving towards them with the emergency lights activated. The police detectives fired at the vehicle, hitting it a number of times.
The police detectives then left the vehicle and exchanged gunfire with the man, and the suspect was shot at multiple times, the police chief added.
At least two unmarked police cars were shot at, officials said.
Brown's commemoration began on Sunday in front of the Canfield Green apartment complex, where he was killed, and was followed by a largely peaceful march through the West Florissant Avenue, the epicentre of protests last year that followed Brown's death.
At the end of the march, led by Brown's father Michael Brown Sr., the protestors released two doves.
Peaceful vigils marked the observance of Brown's death anniversary. Attendees observed four-and-half minutes of silence -- the length of time Brown's body lay on the street after he was shot.
Subsequently, however, demonstrators blocked several streets and clashed with the police.
It was during this time that gunshots were heard, according to various media reports.
White police officer Darren Wilson killed 18-year-old African-American Michael Brown on August 9, 2014 under disputed circumstances, an incident that led to weeks of unrest.
On November 24, a grand jury decided against indicting Wilson in Brown's death, setting off further unrest in the Missouri city.
In another case, no charges were levelled against the police officer involved in the death of Eric Garner, another African-American, who died in July 2014 after the officer put him in a choke-hold.
The two cases triggered widespread protests throughout the country and forced the US government to place racial discrimination by police on top of its agenda.