Story highlights Three men, all civilians, are currently being evaluated

They have shown "no appearance of ill effect," an NYPD official said

New York (CNN) The scene at Trump Tower in New York has been deemed safe after a letter addressed to Donald Trump contained a suspicious white powder, authorities said Thursday night.

The white powder was determined as a primarily non-toxic substance at the scene, said police spokesman Sergeant Brenan Ryan in a statement. Of the four people exposed to the substance -- three men, all civilians, and a police officer -- were evaluated and released Thursday night, Ryan said.

The Department of Health and Mental Hygiene are performing more extensive testing on the white powder and results are expected within the next week, Ryan said.

An intern initially opened the envelope, which was quickly resealed by security, law enforcement officials told CNN Thursday night. They dialed 911 and the New York City Fire Department dispatched a unit to the 5th Avenue building in midtown Manhattan at 8:05 p.m. ET.

Mail is normally opened in the Trump Tower basement before being brought up to its 5th floor offices, a law enforcement source told CNN. But it appears the mail was not screened before being brought upstairs.

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