NEW YORK (AFP) - Thousands of protesters paralysed streets in New York on Thursday to condemn police killings of black suspects as details of a new racially tinged death emerged.

It was the second night of rallies in America's largest city of 8.4 million after a grand jury on Wednesday decided not to indict a white officer for the death by chokehold of an unarmed black father of six children.

National controversy over Eric Garner's death in July and a series of other incidents were fanned further on Thursday by a damning US federal investigation which concluded that police in Cleveland routinely employ "excessive force."

In Arizona meanwhile, police said a white officer shot dead a 34-year-old black during a confrontation outside a convenience store.

Phoenix police said the officer involved shot dead Rumain Brisbon after mistakenly believing he was reaching for a gun inside his jacket. In fact he was unarmed.

The killing is the latest of several cases since the death of Garner in New York in July which have triggered a national debate about how minorities are treated by police and the American criminal justice system.

Police shot dead a 12-year-old boy in Cleveland last month while another grand jury last week decided not to prosecute a white officer in Ferguson, Missouri who killed unarmed black teen Michael Brown in August.

- 'Black Lives Matter' -

Thousands of activists massed in New York's Foley Square, near the city police headquarters shouting "Shut it down" and carrying placards saying "Black Lives Matter" and "Racism Kills."

Police sealed off the Holland Tunnel, the key road link into New Jersey as US media reported that thousands streamed up the west side of Manhattan, clogging streets in downtown Manhattan and shutting traffic on the Manhattan Bridge heading to Brooklyn.

Another group marched across the Brooklyn Bridge, with a black banner that said "this stops today" and 10 black coffins inscribed with names of people killed by police in different city boroughs.

Protests in New York have been overwhelmingly peaceful but police arrested 83 people following Wednesday's decision not to press charges in Garner's death.

At the Manhattan ferry terminal to Staten Island, the New York borough where Garner died, protesters briefly tried to break apart metal barriers erected by police.

But a police spokesman told AFP he would not be able to confirm a number of arrests until after the demonstrations ended.

"Here you can beg for your life but the police will not care," said protester Margarita Rosario, whose 18-year-old son Anthony and nephew were killed by New York police in 1995.

"Nothing will change here until people will react like in Ferguson," said Rosario, who lives in the Bronx.

Smaller scale protests were also staged in Washington, D.C. and Boston on Thursday.

- 'Systemic deficiencies' -

The federal investigation into policing in Cleveland began 18 months ago and was not linked specifically to the killing on Nov 22 of black 12-year-old Tamir Rice in a city playground by police.

Officers responded to a report that a youth was brandishing a gun, but Rice was later found to be carrying a toy, and a video of the incident showed police opening fire within seconds of their arrival.

"We have determined that there is reasonable cause to believe that the Cleveland Division of Police engages in a pattern or practice of using excessive force," US Attorney General Eric Holder said.

He blamed this on "systemic deficiencies, including insufficient accountability, inadequate training and equipment, ineffective policies and inadequate engagement with the community."

Holder has said federal civil rights investigations were being held for both the death of Brown in Ferguson and Garner in New York.

"In recent days, millions of people throughout the nation have come together - bound by grief and anguish - in response to the tragic deaths of Michael Brown... and Eric Garner," Holder said.

"And as President Obama and I have indicated, the time has come to do even more." Barack Obama, America's first black president, briefly addressed the inherent mistrust many black Americans have of police.

"We recognize this is an American problem and not just a black problem or a brown problem," Obama said.