NEW YORK — Record crowds were expected to swarm Manhattan sidewalks and rooftops on Thursday to glimpse the marching bands, floats and massive balloons of Macy’s annual Thanksgiving Day Parade, held under tight security two weeks after the attacks in Paris.

New York officials said about 3.5 million spectators would turn out for the city’s signature parade, in its 89th year, and they urged residents and visitors to carry on with holiday plans, saying there were no credible threats to the city.

“I encourage people to come out. This is a way to push back on events around the world that are meant to intimidate,” Police Commissioner William Bratton said on Wednesday at a press conference in Manhattan near where giant balloons of Snoopy and Hello Kitty were being readied for the event.

The Department of Homeland Security said last week there was no credible threat of an attack on the United States of the type that occurred in Paris. The New York Police Department is ramping up parade security, adding members of a new counter-terrorism unit, officials said.

About 50 million people worldwide were expected to watch the televised parade, in which dozens of giant helium balloons depicting popular cartoon characters, accompanied by floats, volunteers and entertainers, snake through 2.5 miles of Manhattan, ushering in the holiday season and the busiest travel time in the United States.

President Barack Obama sought to reassure Americans on Wednesday they are safe to take to roads, trains and planes over the holiday.

“Right now, we know of no specific and credible intelligence indicating a plot on the homeland,” Obama told reporters at the White House.

A Reuters-Ipsos poll shows Americans have become more concerned about threats since the Paris attacks and now identify terrorism as the most important problem facing the nation.

Jitters have focused on large and heavily-attended events, like New York’s Thanksgiving Day parade. New York City Mayor Bill de Blasio said the city’s police force has been fine-tuning its response to another possible strike since the Sept. 11, 2001, attacks in which the Twin Towers were toppled by two hijacked airliners.

“People should recognize the efforts being made,” de Blasio said at a news conference on Wednesday. “I have absolute faith in the NYPD,” he said.