BALTIMORE (AFP, REUTERS) - Thousands of people demonstrated in major US East Coast cities Wednesday demanding equal treatment for all by police, after a young African American died of injuries sustained in custody in Baltimore.

The biggest show of people power was in Baltimore itself - epicenter of the latest racially tinged unrest to convulse the United States - where several thousand mostly young demonstrators paralyzed 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 and discrimination again bubbled to the surface.

The protests were overwhelmingly peaceful and good-natured, although New York police arrested more than 60 demonstrators, CNN said, and emotions were running high, with scuffles breaking out.

What appears to be a growing movement for change was focused 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 and only small knots of demonstrators remained on the streets when a curfew swept into effect for a second night from 10 pm (10 am Singapore) to 5 am.

'Very encouraged'

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

The circumstances surrounding Gray's death are unclear, but six officers have been suspended with pay.

Adding to the confusion, The Washington Post, citing a police document, said a prisoner sharing a police transport van with Gray told investigators that he could hear Gray "banging against the walls" of the vehicle and believed that he "was intentionally trying to injure himself." The prisoner, who is in jail, was separated from Gray by a metal partition and could not see him, the report said.

Gray died seven days after his arrest with 80 percent of his spine severed at the neck, lawyers for his family say, portraying him as just the latest young African American to die at the hands of the police.

In August, a white policeman shot dead a black teenager in the St Louis suburb of Ferguson, triggering demonstrations in major US cities from Los Angeles to New York that were repeated when a grand jury declined to indict the officer.

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

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

New York arrests

In New York City, police on scooters used batons to try to keep protesters on sidewalks and arrested people who moved into traffic.

Protesters had 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.

New York City police arrested more than 60 people as protesters roved in separate groups through Manhattan, blocking traffic in a few areas. Smaller protests occurred in Boston, Houston, Ferguson, Missouri, Washington, DC, Seattle and a handful of demonstrators were arrested in Denver.

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, a 17-year-old African American, 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'

Among the many startling images to emerge from Baltimore 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.