Police evacuated the 11th floor of Hillary Clinton’s Brooklyn campaign headquarters Friday night after a white powder was found inside a letter, an NYPD spokesman said.

The unknown substance preliminarily has been deemed nonhazardous, the spokesman said Saturday morning.

The envelope and powder have been taken to a laboratory for further testing and evaluation, he said.

The letter was first opened by two interns at Clinton’s office in midtown Manhattan on 45th Street about 5:30 p.m., police said, and taken to the Brooklyn office at One Pierrepont Plaza in Brooklyn Heights shortly after. Of four people at the Brooklyn location exposed, no one was hospitalized, and there has been no report of sickness, illness or injury, police said.

The police spokesman said he did not know to whom the letter was addressed or if there was a return address, or what any accompanying letter may have said.

“Hillary for America notified law enforcement Friday evening of an envelope containing a suspicious substance,” said Hillary for America senior national spokesman Glen Caplin.

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“The four individuals involved have reported no health issues and, following a full examination by medical personnel, were each released to go home,” Caplin said. The “office remained open throughout this period” and remained open Saturday, he said.

Police said the incident remains under investigation.

The NYPD’s Emergency Services Unit, Office of Emergency Management and the Secret Service were on scene Friday night.