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Demonstrators with signs reading "Not my president!" clogged streets in New York City on Saturday during a fourth day of anti-Trump protests nationwide, a day after a person was shot during a protest in Portland, Oregon.

Two 18-year-old men detained early Saturday were arrested later in the day in connection to the shooting on Portland's Morrison Bridge, which occurred after 1 a.m. local time (4 a.m. ET) Saturday, police said. It was unclear whether the shooting was politically motivated.

PHOTOS: Scenes of Fury as Anti-Trump Rallies Turn Violent

"Preliminary information indicates that a suspect was in a vehicle on the bridge and there was a confrontation with someone in the protest," Portland police said in a statement. "The suspect got out of the vehicle and fired multiple shots injuring the victim." The victim is expected to survive, police said.

The arrests were made after an off-duty officer spotted a suspect vehicle and detained four people who are believed to be "criminal gang associates," police said. A firearm was found in the vehicle, police said.

Earlier, police reported that "burning projectiles" were being thrown at officers during one of three demonstrations that occurred simultaneously in the city.

The gunshots came on the fourth night of protests in Portland. Protesters hit the streets again Saturday on a fifth night of demonstrations since the election. There were three arrests, police said.

On Thursday, a similar rally boiled over into what police described as a "riot" after some demonstrators armed with bats smashed stores and cars, and others lit fires.

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Elsewhere overnight Friday, marchers blocked a major roadway in the Miami area and hundreds gathered in Atlanta, Boston and other cities.

By early Saturday in New York, a total of 11 arrests were reported.

A larger protest that was organized Saturday afternoon began in Manhattan's Union Square and ended at Trump Tower in midtown, where demonstrators stopped and chanted in front of the skyscraper where Trump resides and was meeting with visitors. A law enforcement source said the protest at its peak had an estimated 25,000 participants.

"We reject the president-elect!" the crowd chanted along Fifth Avenue.

Among the sea of police officers, protesters and gawkers at Trump Tower were some familiar faces.

Filmmaker Michael Moore showed up at the president-elect's iconic Fifth Avenue landmark, live-streaming his visit as he made his way as far into the building as he could before security stopped him.

Trump is is an "illegitimate president and does not have the vote of the people," Moore told NBC News as he ascended up the floors of the ornate building that bears Trump's name in gold on the front of it.

Moore, who was wearing a safety pin as a show of solidarity for minorities and women who feel threatened after Trump's election, was stopped on the fourth floor when he asked to meet with Trump.

"You'd have a to check with his staff," a secret service agent told him.

A protester on Fifth Avenue in New York City on Nov. 12, 2016. Yasmin Merchant

Moore settled on leaving a handwritten note for Trump that said: "Mr. Trump I'm here. I want to talk to you" before he got into a debate with a Trump supporter in a "Make America Great Again" hat and then left the building.

Other big names seen at the building Saturday included chairman of the Republican National Committee Reince Priebus and interim leader of the U.K. Independence Party Nigel Farage.

The visitors come as Trump is picking his transition team, which Trump put Vice President-elect Mike Pence in charge of on Friday.

When asked if he was there for transition talks, Farage told NBC News: "We're just tourists."

But the protests outside also drew some in favor of Trump, and they held signs that read, “He is My President,” “Hillary for Prison” and “Crybabies.”

Another protest took place Saturday morning in downtown Los Angeles, where approximately 8,000 gathered — according to the LAPD — after more than 180 people were arrested Friday night.

Protesters hold up signs during a march and rally against the election of Donald Trump in Los Angeles on Nov. 12. LUCY NICHOLSON / Reuters

Demonstrators hit the streets in Miami, Birmingham, Alabama, and Fresno, California, as well as internationally. Hundreds reportedly gathered in Berlin at the Brandenburg Gates, some with anti-Trump messages.

In Indianapolis, three people were arrested and two police officers were injured after rocks were thrown at police during an anti-Trump demonstration downtown, police and NBC affiliate WTHR reported.

IMPDNOW: 3 arrests and 2 officers injured after protesters threw rocks at officers trying to keep the peace in downtown. — IMPD (@IMPD_News) November 13, 2016

A vigil to promote solidarity after the election was held at Lafayette Park adjacent to the White House Saturday. Those in the crowd held LED tealights and glow sticks, and sang songs like "Hallelujah," All You Need Is Love" and "Imagine."