Representatives from nearly 200 countries will descend on New York City this week as leaders converge on Midtown East in Manhattan for the annual session of the United Nations General Assembly, bringing motorcades — and therefore, traffic — with them.

A gridlock alert is in place from Sept. 21 to Sept. 25, Mayor Zohran Mamdani said. Rolling pedestrian and vehicle closures will take place around the United Nations Headquarters, spilling out across the city as delegations traverse the city. Portions of F.D.R. Drive will be closed, and ferry service will be disrupted, the mayor said. Police Commissioner Jessica Tisch said that from Sept. 20 through Sept. 26, First Avenue will be closed between 41st and 48th Streets, while 44th Street to 47th Street will be closed between First and Second Avenues. Each day until the end of the session, around 9 p.m., 42nd Street will close between First and Second Avenues. The 42nd Street exit from F.D.R. Drive will also be blocked off.

There are no known specific threats to this year's General Assembly, but officers will secure hundreds of motorcades as heads of state and high-ranking officials move between hotels, U.N. buildings and meetings around the city. This is one of the most complex security operations that the N.Y.P.D. carries out. The mayor recommended that commuters use public transportation. There will be protests as well, generally contained to Dag Hammarskjöld Plaza, but demonstrations are planned at Bryant Park, Union Square and in Brooklyn. As always, the N.Y.P.D. will facilitate First Amendment activity with no tolerance for violence or destruction of property.