"We're in the hundreds here, probably started around a thousand," she said.
Demonstrators were gathering near the decommissioned USS Intrepid aircraft carrier on Manhattan's West Side, where Trump was slated to speak Thursday evening.
Trump is speaking at the Intrepid museum to honor the 75th anniversary of the Battle of the Coral Sea, during which the U.S. and Australian forces fought together against the Japanese in World War II.
Trump is also meeting with Australian Prime Minister Malcolm Turnbull after he makes his remarks. Trump pushed back his meeting several hours as the House voted Thursday on the GOP's plan to repeal and replace ObamaCare.
House Republicans narrowly passed the measure on a 217-213 party-line vote, with 20 Republicans bucking their party and voting against the plan.
Trump's presidential opposer, Hillary Clinton, who formerly served as a senator from New York, won the state by 59 percent to Trump's 36.5 percent in November.
Trump highly unpopular in Manhattan itself, where the protesters demonstrated against him Thursday. Nearly 87 percent voted for Clinton compared to his almost 10 percent.
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