(CNN) White powder that was sent to Hillary Clinton's campaign office in New York tested negative for harmful substances in a preliminary investigation, police said.
Clinton campaign workers had opened an envelope containing the white substance Friday, police said.
The envelope had first been delivered to Clinton's midtown Manhattan office and opened there, said Lt. Thomas Antonetti of the New York Police Department. It was then transferred to her Brooklyn campaign headquarters. The reason why it had been taken there was unclear.
But it resulted in the evacuation of the building's 11th floor during the evening. Another floor used by the Clinton campaign in the building remained operational during the incident.
"The four individuals involved have reported no health issues and, following a full examination by medical personnel, were each released to go home," said Clinton campaign spokesman Glen Caplin in a statement.
Federal and local officials found the substance "to be non-hazardous," according to the statement.
"Our office remained open throughout this period and will remain open without interruption (Saturday) morning," said Caplin.
The NYPD is investigating the incident. The U.S. Secret Service and the Office of Emergency Management are also involved, according to the NYPD.