Pope Francis spoke at the opening plenary session before the world leaders took to the stage for their summit.
Several streets around the UN were blocked off to traffic and pedestrians were not allowed in without credentials or proof of living in the area.
Many with credentials were made to take long diversions to get to the appropriate UN entrance.
Package delivery services warned customers that in some areas there would not be deliveries till next week.
Boats from security forces patrolled the East River behind the UN building.
Visitors were subjected to at least three searches before they could enter the General Assembly hall.
Personnel from half-a-dozen New York City and federal law enforcement agencies were deployed for the security operations. They were backed by bomb-sniffing dogs, also from various agencies.
Post boxes and trash cans in the area around the UN were removed for fear of being used to hide explosives.