Suspicious White Powder Sent to Donald Trump Not Hazardous: Officials The powder was inside an envelope addressed to the GOP front-runner.

 -- Law enforcement sources confirm to ABC News that established protocol for opening letters was not followed when a suspicious white powder was discovered at the Trump Tower in Manhattan Thursday night.

The incident prompted the New York Fire Department, the New York Police Department and EMS workers to investigate -- but the powder was deemed not hazardous, according to the NYPD.

Mail is normally opened in the basement mailroom and then brought to the fifth floor. The letter was opened on the fifth floor, which is in violation of protocol established for opening mail. There were six workers in fifth-floor offices at the time the letter was opened.

Samples were taken, however, from the scene for further testing.

According to the NYFD, the first responders were called to the Fifth Avenue high-rise around 8:15 p.m.

ABC-owned WABC in New York previously reported that the powder was found in the mailroom, in an envelope with a letter addressed to GOP presidential front-runner Donald Trump. The letter was opened by one of Trump's staffers, according to WABC.

A Trump campaign source tells ABC News the fifth-floor offices were evacuated after the discovery, but most of the staff had left for the day.

Aaron Katersky contributed to this report