Senator Bernie Sanders' Burlington office was evacuated Thursday after police deemed a package delivered there to be suspicious, authorities said. Burlington police said in a press conference that the suspicious package was not an explosive device and was deemed "harmless."

Sanders was in New York City on Thursday for a taping of "The Late Show with Stephen Colbert." His 2020 campaign stated they do not comment on matters of security.

Police said it was unclear what was in package and who sent it. The U.S. Post Office will be launching an investigation.

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Investigators were called around 11:45 a.m., CBS Burlington affiliate WCAX-TV reports. The building was evacuated around 4 p.m., the station said.

Burlington police tweeted state police had responded as well.

Along with @VTStatePolice, @OneNorthAvenue has responded to a suspicious package at the office of Senator Sanders. Out of an abundance of caution, we have cleared offices in the building while it is assessed. Updates to follow. — Burlington Police (@OneNorthAvenue) September 26, 2019

Burlington Deputy Police Jon Murad described to WCAX-TV the criteria that would prompt the evacuation.

"Addresses that are slightly off or people who are the intended recipient of the device who no longer work at the office," Murad told WCAX-TV. "They include packages that have had too much postage put on them. They include packages that have been taped or closed in strange ways. They include packages that may have both signage or symbolism on the exterior that are indicative of trouble or of messages that are beyond what a normal package would have and make the package suspicious, hence suspicious package. But I can't talk about this specific one simply because it is an ongoing investigation. However, I will say that it met many of those things and that was why we spent a lot of time looking at it."

It's the second time this month authorities have investigated packages at Sanders' offices, according to WCAX-TV. On September 11, authorities responded to his St. Johnsbury offices for an incident that turned out to be a false alarm.

Suspicious package was intercepted at Senator Bernie Sanders' Burlington office Thursday, September 26, 2019. WCAX-TV

Cara Korte contributed reporting.