Hundreds of protesters chanted and waved signs to voice their outrage at Republican front-runner Donald Trump outside the New York venue where he and his two rivals for the presidential nomination gathered for duelling speeches.
Inside a hotel near Grand Central Terminal on Thursday, Trump, US senator Ted Cruz of Texas and Ohio Governor John Kasich were addressing a New York state Republican Party gala as they campaign for the state's primary contest on Tuesday.
A group of the protesters stormed the mezzanine of the Grand Hyatt with a banner that read: "NYC Rejects the Party of Hate". Eleven of them were reported arrested.
Outside the hotel, many anti-Trump demonstrators called the New York billionaire businessman a fascist or white supremacist.
They even teased him about his signature hairdo.
"We Shall Over Comb," read one sign. Others said: "Deport Trump", "No allegiance for Trump" and "Black lives matter".
Trump has drawn many protests for policy positions that include building a wall along the US border with Mexico, deporting 11 million illegal immigrants and banning Muslims temporarily from entering the US.
A series of speakers addressed the protest crowd with a loudspeaker. Police set up portable barriers to keep protesters separated from traffic and allow pedestrians to pass on busy 42nd Street.
"Although Trump is from here, there is no place for him here," said one of the speakers, Nabil Hassein, 27, of the group Millions March NYC.
Kasich scored a victory with the endorsement of former New York governor George Pataki, an unsuccessful candidate for the Republican nomination for the November 8 election.
But all signs point to a Trump victory in New York, a win that would help ease the pain of a loss to Cruz in Wisconsin last week and Cruz's outmanoeuvring of Trump to sweep all the Republican delegates in Colorado.
The Trump campaign got some good news when a Florida prosecutor announced that Trump's campaign manager, Corey Lewandowski, would not be prosecuted on a misdemeanour battery charge involving a reporter he was accused of grabbing at an event last month.
Trump, a staunch anti-establishment candidate, is responding to the challenge from Cruz by taking steps to reset his campaign to try to draw in more support from establishment Republicans.
A top Trump adviser met in Washington with the candidate's congressional supporters. The aide, Ed Brookover, told the lawmakers how they could help Trump on his "glide path" to the nomination.
Brookover told about a half-dozen lawmakers who have endorsed Trump how the front runner would win the 1237-delegate majority he needs to become the nominee.
Some establishment Republicans, alarmed at Trump's comments on immigration and trade, are hoping to force a contested convention by denying him the delegates needed to win.
Lawmakers at the meeting told Reuters they came away feeling comfortable that Trump can get the delegates he needs to clinch the nomination ahead of the party's July 18-21 convention in Cleveland. More meetings will be held in the coming weeks.
The lawmakers said Brookover explained how conservative estimates showed that Trump would likely secure 1265 delegates - more than needed to win the nomination.
