BALTIMORE (AFP) - Protesters targeted businesses and smashed police cars in downtown Baltimore on Saturday as the biggest demonstration yet over the death of a young African-American man in police custody turned violent.
More than 1,000 people had joined an orderly 90-minute rally at Baltimore city hall demanding justice for Mr Freddie Gray, 25, who died last Sunday from spinal injuries, a week after his arrest in the city's impoverished west side.
But the mood shifted dramatically when scores of protesters moved to the vicinity of the Camden Yards baseball stadium, scene of a twilight Baltimore Orioles-Boston Red Sox game. Live images from local television news helicopters showed a crowd hurling soda bottles and trash cans at police officers.
"Protesters are now breaking windows and throwing items at us," the Baltimore police department confirmed on its Twitter feed. "We are asking everyone to remain peaceful."
Others were seen looting a 7-Eleven convenience store, smashing a Michael Kors storefront, and blocking intersections, with one motorist getting a rock through her car window, NBC affiliate WBAL reported.
Five police cars were seen by an AFP photographer getting their windows smashed, before riot-equipped police intervened.
Twelve people were arrested, police commissioner Anthony Batts told reporters, as police in riot helmets went face-to-face with protesters, ordering them to disperse.
Another police spokesman blamed the trouble on "isolated pockets" of individuals who were believed to have come from out of town.
Fans at the baseball game, which went beyond the standard nine innings due to a tie, were told to remain in the stadium, "due to an ongoing public safety issue".
Later in the evening, dozens of police formed a cordon around the Western District police station, scene of nightly protests since Mr Gray died. NBC affiliate WBAL reported two arrests, witnessed from its news helicopter.
Tensions have been simmering in the blue-collar Mid-Atlantic port city of 620,000 as investigators try to establish the circumstances that led to Gray's death.
Speakers at the city hall rally called for President Barack Obama to launch a national inquiry into police misconduct, following a series of fatal confrontations between white police officers and African-American men and boys.
"It has to stop. It really has to stop because it could have been any one of us," a young male adult member of Mr Gray's extended family told the crowd.
In a press conference on Friday, officials acknowledged Mr Gray should have received medical help at the moment of his arrest, when he was seen by bystanders - and caught on video - howling in apparent pain.
They also revealed that Mr Gray, contrary to police department policy, was not buckled into his seat in the van, which made at least three unexplained stops on its way to the Western District police station.
Mr Gray died on Sunday with 80 per cent of his spine severed at the neck, lawyers for his family have said. His funeral is scheduled for Monday.
Six officers have been suspended with pay as the police investigation inches closer to a May 1 deadline to submit findings to a Maryland state prosecutor, who could decide to press charges.
Mr Gray's death is the latest in a string of high-profile confrontations between African-Americans and the police, including the fatal shooting of unarmed teenager Michael Brown in August in the St Louis suburb of Ferguson.