Thousands of demonstrators disrupted New York City traffic into early today after a grand jury decided not to bring charges against a white police officer in the chokehold death of an unarmed black man.

Mostly peaceful protests sprung up on Wednesday evening at locations throughout Manhattan, including Grand Central Terminal, Times Square and near Rockefeller Centre, after the panel returned no indictment against Officer Daniel Pantaleo in the death of Eric Garner in July. The US Justice Department said it was investigating to determine whether Garner's civil rights had been violated.

The 43-year-old father of six was accused of illegally selling cigarettes on a sidewalk when Pantaleo put him in a chokehold from behind and tackled him with the help of other officers. Police said he had resisted arrest. The city's medical examiner had ruled the death a homicide.

The deadly encounter on Staten Island, New York City's least populous borough, was captured on a video that quickly spread over the Internet and fuelled debate about how US police use force, particularly against minorities.

President Barack Obama said the grand jury decision spoke to "the concern on the part of too many minority communities that law enforcement is not working with them and dealing with them in a fair way".

The decision poses the biggest challenge yet for New York Mayor Bill de Blasio, who came into office in January promising to mend strained relations between black New Yorkers and the police department.

It was the second grand jury in just over a week to decline to prosecute a white policeman in the death of an unarmed black man. The decision by a panel in the shooting death of black teenager Michael Brown in Ferguson, Missouri, sparked a spasm of violence, with businesses burned and looted in the St. Louis suburb.

By contrast, the New York protests were civil, with about 30 arrests by mid-evening. Police were clearly showing restraint and allowing demonstrators to block traffic briefly before coaxing them to move on.

Marchers snaked through the streets for hours, chanting and bumping up against throngs of tourists in New York for the holiday season. Disparate clusters of protesters crossed through Times Square a number of times, and one group brought traffic on the West Side Highway along the Hudson River to a standstill.

Later, after marching from Central Park to lower Manhattan, some protesters crossed a bridge into the borough of Brooklyn.

Keiha Souley, 35, was driving his taxi cab on Broadway when protesters blocked traffic. As he chanted along with demonstrators, he said he did not mind the delay.

"You've got to stand up sometime," he said.

In one of several "die-ins", demonstrators laid on the pavement in silent protest about a block from where the Christmas tree lighting ceremony was under way at Rockefeller Centre. Police blockaded the street, preventing marchers from interrupting the nationally televised event.

About a thousand people packed into the ornate main hall of Grand Central Terminal for a noisy but peaceful protest.

On Staten Island, near the site where Garner was apprehended, Daniel Skelton, a black 40-year-old banker, spoke loudly as he voiced his outrage: "A black man's life just don't matter in this country."

Garner's stepfather Benjamin Carr, also at the scene, consoled another angry man in a car.

"We don't want no Fergusons here," Carr said. "All we want is peace."

The Justice Department said it would investigate the Garner case. It is already probing the circumstances of the Missouri shooting.

"Our prosecutors will conduct an independent, thorough, fair and expeditious investigation," US Attorney General Eric Holder told reporters in Washington. "In addition to performing our own investigative work, the department will conduct a complete review of the material gathered during the local investigation."

Legal experts say that while there is no explicit law against chokeholds, their use is prohibited by New York police regulations. Any violation, however, would not necessarily constitute a crime, they said. The Patrolmen's Benevolent Association, the municipal police union, said officers involved in the Garner incident acted within the scope of the law.

Mayor de Blasio praised New York Police Commissioner Bill Bratton's efforts to bridge a long-standing divide between police and minority groups, but de Blasio also said he had warned his African-American son to take "special care in any encounters with police officers".

In a statement released by the police union, Pantaleo expressed his condolences to Garner's family.

"It is never my intention to harm anyone and I feel very bad about the death of Mr Garner," he said.

But at a news conference, Garner's widow Esaw Garner rejected Pantaleo's sympathies.

"There's nothing that him or his prayers or anything else will make me feel any different. No I, don't accept his apologies.

"He's still working. He's still getting a paycheck. He's still feeding his kids," she said. "And my husband is six feet under and I'm looking for a way to feed my kids now."

Pantaleo, an eight-year NYPD veteran, testified at the grand jury. While that is a rarity in grand jury proceedings to decide whether there are reasonable grounds for an indictment, prosecutors have discretion to put a police officer accused of misconduct on the stand. The officer in the Michael Brown shooting also testified to the Missouri grand jury.

It is uncommon for either federal or state prosecutors to charge a US police officer for excessive force, even when a death results.

The US Supreme Court and lower courts have ruled over decades that police officers should have wide latitude to use violence to defend themselves and to take suspects into custody.

In ruling Garner's death a homicide, the city medical examiner said police officers killed him by compressing his neck and chest. His health problems, including asthma and obesity, were contributing factors, the medical examiner said.

The video of Garner's arrest shows him arguing with police officers, saying, "Please leave me alone," and later, "Don't touch me," before Pantaleo puts him in a chokehold. With officers holding him down, Garner pleaded with them, saying repeatedly, "I can't breathe."