The security scare came ahead of the session on Haiti with former US president Bill Clinton.
"A suspicious envelope was found in the cafeteria. In response they have closed the cafeteria and that area has been contained. The (UN) Department of Safety and Security is working with the host country to investigate the matter," said UN spokesman Farhan Haq.
Though the finding of a white powder was not mentioned by UN officials, a New York City police spokesman, Marc Nell informed that the police received a call about a suspicious white powder in the ground-floor cafeteria.
As part of the security measure, a scheduled appearance of Clinton, UN envoy to earthquake-ravaged Haiti, at the United Nations was postponed from 4 pm to around 5 pm.
Similar envelopes containing a suspicious white powder were sent to the UN missions of Austria, France, Germany and Uzbekistan in Nov 2009.
Since 2001, US authorities have been on alert about mail with white powder since envelopes laced with anthrax were sent to media outlets and US lawmakers, which claimed five lives.