Seven people were exposed to a suspicious white powder in a U.S federal building in downtown Manhattan on Wednesday, authorities said.

The offices of the Social Security Administration on the 40th floor of the building -- which houses several agencies including the Federal Bureau of Intelligence and U.S. Citizenship and Immigration Services -- were evacuated.

"There was a mailing that was opened at 2:15 p.m. in the offices of the SSA (Social Security Administration)," said FBI spokesman Jim Margolin. "It contained a white powder that was contained and isolated and will be analyzed."

He said the results of the analysis would not be immediately known.

New York Fire Department spokesman Jose Costa said seven people were exposed to the white powder.

U.S. authorities have been on alert for mail with white powder in it since 2001, when envelopes laced with anthrax were sent to media outlets and U.S. lawmakers, killing five people.

In November, the U.N. missions of several countries received letters containing white powder that turned out to be flour. At least 40 people were decontaminated as a precaution. Similar scares have hit New York-based companies and institutions. (Reporting by Basil Katz; editing by Michelle Nichols and Cynthia Osterman)