A letter addressed to Donald Trump at his campaign office in Trump Tower in Manhattan contained a suspicious white powder, law enforcement officials told CNN Thursday night.
The envelope was opened by an intern, who discovered the substance before security resealed it and notified authorities.
A spokesman for the New York Fire Department said a unit was dispatched to the 5th Avenue building at 8:05 p.m. ET.
Five civilians and one police officer are currently isolated and being monitored by authorities, the spokesman said, though no one appears to be sick or injured.
The New York Police Department says it is currently investigating the incident.
Trump is in Costa Mesa Thursday night. His presidential campaign did not immediately respond to a request for comment.