The anxiety and unrest that has crippled Baltimore spilled over into the Big Apple Wednesday as more than 120 people were arrested across Manhattan in scuffles with cops during protests over the death of Freddie Gray, sources said.

Hundreds of demonstrators, who first gathered at Union Square for what was supposed to be a peaceful rally, erupted into a free-for-all in the streets at about 7:30 p.m. as groups splintered off to create havoc around town.

“What do we want? Justice! If we don’t get it? Shut it down!” protesters chanted as officers started to detain people and corral them in police vans.

The demonstration was billed as a show of support for protesters in Baltimore, where a nightly curfew was imposed this week following riots sparked by Gray’s death from injuries suffered while in police custody.

From Union Square, protesters marched along East 17th Street toward Fifth Avenue before being stopped by police.

An NYPD helicopter hovered overhead and a police loudspeaker warned protesters that they would be arrested if they marched in the street.

As some protesters resisted arrest, cops carried them by their limbs and shackled them.

Other protesters trying to breach barricades were shoved back by cops.

Then rowdy agitators began to push back at cops and some even started throwing punches along 17th Street and Fifth Avenue, where dozens of ­arrests were made.

The protest then split off into factions. Some marched toward the Holland Tunnel, where outbound traffic was briefly halted. Others took to the West Side Highway and marched up to Times Square.

“Black lives matter. No justice, no peace,” protesters chanted as they marched through Times Square.

Meanwhile, in beleaguered Baltimore, the second night of a state-imposed curfew went mostly without incident as concerned members of the community formed groups and urged citizens to head home and not partake in violence.

In Washington, DC, protesters stood in front of the White House with signs bearing slogans in support of Gray and Michael Brown, who was shot dead by police in Ferguson, Mo., last year.

Protests returned to Ferguson as well — one day after looting, fires and gunfire in Baltimore protests over Gray.

Baltimore Mayor Stephanie Rawlings-Blake defended her handling of the situation in her city, denying a report that she had told police commanders to “stand down” and let protesters vent their rage.

Rawlings-Blake, 45, a Democrat, said state officials were involved in decision-making from the beginning — and she mocked Republican Gov. Larry Hogan’s claims that he didn’t receive return phone calls from her as the riots unfolded Monday afternoon after the funeral for Gray.

“When he has people right there in the [emergency operations] center with us, the notion that he didn’t get a call back from me directly . . . that’s absurd,” the mayor said as tensions showed signs of easing in the city.

A senior law enforcement source told Fox News that Rawlings-Blake had ordered her officers to stand down as the rioters torched buildings and cars and looted stores.

Asked if Rawlings-Blake had been responsible for the order, the source said, “You’re goddamn right [she] was.”

Later, when asked by Fox News if there had been a “hold-back” order to police, Rawlings-Blake said, “No . . . you have to understand, it’s not ‘holding back.’ It’s ­responding appropriately.”

Kevin Harris, a spokesman for Rawlings-Blake, said, “What we’ve always tried to say is, this is a very fluid situation. We will use these tools [curfews] as long as they’re needed.

“But the second it comes that we feel they’re not needed anymore, we won’t keep the curfews in place and we won’t keep the National Guard here.”

New US Attorney General Loretta Lynch, meanwhile, condemned the rioting, calling it “senseless acts of violence.”

Additional reporting by Natalie Musumeci and Ben Feuerherd