BALTIMORE, United States (AFP) – Protesters defied a citywide curfew that launched into effect in Baltimore on Tuesday as nervous authorities attempted to stave off another night of violence, in the latest race-related unrest to roil the United States.

It was not immediately clear how successful the emergency night-time curfew was, but television footage showed knots of mainly young, black men still out on the streets after the 10:00 pm (0200 GMT) order time. It was to be lifted at 5:00 am and in place for a week.

Police said they would enforce the curfew, but minutes after it kicked in they had not moved on demonstrators, whose number was put at “several hundreds” by CNN.

National Guard troops have deployed to the gritty port city of 620,000, where violence and looting erupted on Monday after the funeral of 25-year-old African-American man Freddie Gray, who died after suffering severe spinal injuries during a police arrest.

Speaking in nearby Washington, President Barack Obama warned that recent incidents “raise troubling questions” about the policing of black communities in the United States.

Obama condemned Monday’s rioting, but also said that a series of incidents — beginning last year with the police shooting of an unarmed black teenager in Ferguson, Missouri — was worrying.

“Since Ferguson… we have seen too many instances of what appears to be police officers interacting with individuals — primarily African American, often poor — in ways that raise troubling questions,” the president said.

“I think there are police departments that have to do some soul-searching,” added Obama, the first black president of the United States.

“I think there’s some communities that have to do some soul-searching. I think we as a country have to do some soul-searching. This is not new. It’s been going on for decades.”

 – Reinforcements –

 In Baltimore, thousands of military and police reinforcements swarmed onto the streets after a night of unrest saw stores looted, more than 140 vehicles burned, 20 police wounded and more than 250 suspects arrested.

There were tense scenes earlier Tuesday when noisy supporters faced off against police lines. Police made arrests and pepper spray was deployed at least once, though confrontations were mostly sporadic.

Maryland Governor Larry Hogan inspected a National Guard barricade and vowed to “make sure what happened last night in Baltimore City is not going to happen again.”

“Tonight we will have 2,000 National Guardsmen and over one thousand law enforcement officers on duty,” he later told reporters.

The initial trigger for the violence came after a dignified service for Gray, who died a week after his spine was all but severed as he was detained by city police.

An investigation has been launched into the cause of his injuries, but many see the incident as only the latest example of police brutality against black suspects.

 – Distrust of police –

 Volunteer clean-up teams hit the streets Tuesday and residents spoke of their terror as gangs roamed the streets fighting police and destroying property.

“It was horrific to the point where my children were actually crying, trying to get back to the house, because there was so much going on,” Latania Graham told AFP.

Many condemned the rioters, but also spoke of their distrust of police.

Department store clerk and Baltimore native Aretha Williams, 45, speaking in front of a line of mostly white police officers in riot gear, said: “I think that a lot of the police are racist… they get a license to kill by becoming a police officer.”

A 68-year-old retiree who gave his name as Clarence said he hadn’t seen Baltimore so tense since the riots of 1968, when six people were killed, 700 injured and much of the downtown area razed.  

“The police brutality. That’s sad. You have a man handcuffed. You don’t beat him,” he said. “You’ve got some good ones out there. But it seems like it’s getting worse.”

 – Spinal injuries –

 The Orioles, the city’s baseball team, cancelled games against Chicago’s White Sox on Monday and again on Tuesday. Wednesday’s game will take place in an empty stadium, in what is believed to be the unprecedented step of ordering an MLB game played behind closed doors.

Last year’s fatal shooting of unarmed teenager Michael Brown by a white police officer in Ferguson triggered coast-to-coast protests.

Lawyers for Gray’s family say his death was caused by injuries sustained following his arrest. He lost consciousness in custody, and died within a week.

Six officers have been suspended pending the outcome of a police investigation that is to be submitted to state prosecutors by Friday.