New York police had no immediate confirmation of the nature of the incident.
A film installation celebrating the words of Mandela is taking over the electronic billboards in the square for a few minutes every night until May.
Senior White House officials believe Times Square car bomb was the work of a Pakistani Taliban group, rather than a "lone wolf" attacker.
US authorities were still questioning a Pakistani-American man on Wednesday, who they say admitted trying to bomb New York’s Times Square.