Baltimore, United States: Thousands of people demonstrated in major cities along the US East Coast on Wednesday demanding an end to what they say is police brutality, after a young African-American man died of injuries sustained in custody in Baltimore.

The biggest show of people power was in Baltimore itself, where several thousand mostly young demonstrators paralyzed several city blocks in a major rally through downtown to City Hall.

Thousands more protested in New York, the capital Washington and Boston in solidarity, as decades-old simmering anger over police tactics -- particularly in their dealings with black Americans -- again bubbled to the surface in the United States.

The protests were overwhelmingly peaceful and good-natured, although New York police detained several demonstrators and emotions were running high.

What appears to be a growing movement for change was centered on Baltimore, where a rally that started at the main train station included black and white demonstrators, some of them linking arms and chanting: ‘No justice, no peace! No racists, no peace!’

Many in the march were high school or college students.

‘We're protesting the ongoing injustices that police have perpetrated on black men particularly. Police are trigger-happy and we need to stop that,’ Jonathan Brown, 19, a student at Johns Hopkins University, told AFP.

Some in the huge crowd held placards, one reading, ‘Killer cops deserve cell blocks.’ A few wore shirts with the words, ‘Amnesty International observer.’

The 2,000 National Guard personnel who have flooded Baltimore this week kept a low profile, although authorities have said they are primed to enforce a curfew that will sweep into effect for a second night from 10:00 pm (0200 GMT Thursday) to 5:00am.

Police used loudspeakers to urge the crowds to go home and initial signs were that most of the demonstrators would be off the streets for the curfew.

'Very encouraged'

The Baltimore rally was a far cry from the violence and looting which flared there following the funeral of Freddie Gray, 25, on Monday.

Gray's death was the latest instance in the United States of a black man succumbing at the hands of police -- a situation that has stirred resentment among African Americans who believe they are targeted by police.

That anger also sparked coast-to-coast demonstrations in major US cities last year after a white policeman shot dead an unarmed black teenager in the St Louis suburb of Ferguson in August.

Maryland State Governor Larry Hogan said he had been ‘very encouraged’ by the last 24 hours and said a semblance of normality was returning to Baltimore, a gritty city of 620,000 about an hour's drive from Washington.

But he cautioned: ‘We are not out of the woods yet.’

And he warned demonstrators to respect the curfew: ‘There are peaceful protests happening tonight. We want to make sure individuals can exercise their First Amendment rights and express their concerns.’

New York arrests

In New York, protesters gathered at Union Square, in Lower Manhattan, for a rally dubbed on a Facebook page, ‘NYC Rise up and Shut it down with Baltimore.’

The large march initially met no resistance from police, but that swiftly changed as officers -- who deployed in significant numbers -- moved in and made arrests.

The New York Police Department would not say how many were detained, though CNN put the number at a couple dozen.

In Washington, there was a festive atmosphere as a well-organized march that peaked at about 1,000 ended at the White House, where protesters chanted and held signs reading, ‘Stop racist police terror.’

Miyeah Cook, 17, told AFP: ‘I'm just trying to stand up for black people everywhere. Just anywhere and everywhere.

‘Honestly, I don't know why I'm out here at this point because we're literally being escorted by the police. I don't find it helpful at all.

‘It honestly made me mad once I found out that the police were everywhere we went.’

'Just lost it'

Baltimore police made 18 arrests during the day on Wednesday, said Police Commissioner Anthony Batts, and they were keeping a keen eye on social media -- used by protesters to coordinate their action.

Among the many startling images to emerge from the riots in the city was that of an infuriated mother hitting her teenage son repeatedly for joining the demonstrations on Monday and dragging him away.

‘I just lost it,’ said Toya Graham, a single mother of six, whose actions have been widely praised.

‘I was shocked, I was angry, because you never want to see your child out there doing that,’ she added, speaking to CBS News.