Clinton's Brooklyn Campaign HQ Evacuated After Suspicious Substance Discovered in Letter

— -- Hillary Clinton's campaign headquarters in Brooklyn, New York, were evacuated Friday night after a pair of interns discovered a suspicious substance inside a letter, police have confirmed.

The substance has not yet been determined, but it has been deemed not hazardous, since there have been no reports of illness nor any complaints from anyone exposed, the NYPD confirmed to WABC-TV.

Four people were exposed to the substance, which was contained in a standard No. 10 envelope, the NYPD said.

The NYPD confirmed to ABC News that two interns discovered the suspicious substance in an envelope at 5:30 p.m. in Clinton's Manhattan office. The interns then brought the letter to the 11th floor of the campaign's 80,000-square-foot Brooklyn headquarters, located in the borough's Brooklyn Heights neighborhood.

Clinton was not present at the office, according to the NYPD.

The investigation is ongoing.

ABC News' Andrew Evans and Jamie Hoskins contributed to this report.