One floor of Democratic presidential candidate Hillary Clinton's national campaign headquarters was evacuated Friday evening after a white powdery substance caused a security scare.

The New York Police Department said the substance was discovered in an envelope opened by two interns at Clinton's Manhattan office at around 5:30 p.m. It was then taken to the 11th floor of her Brooklyn headquarters.

The New York Post reported that emergency services ordered the floor to be evacuated after four people were exposed to the substance.

An NYPD spokesman declined to identify the substance, but said that tests showed it was not harmful.

Clinton campaign spokesman Glen Caplin said that the four people who were exposed to the substance had not reported any health problems and were allowed to go home.

"Our office remained open throughout this period and will remain open without interruption [Saturday] morning," Caplin said.

The Associated Press contributed to this report.