Envelopes containing white powder was opened inside a federal building in lower Manhattan, according to a source familiar with the matter, prompting a police response.

The five envelopes were discovered in a mailroom inside 26 Federal Plaza, a source told NBC New York. About a half a dozen people were nearby when the powder spilled out, but officials said only two people were directly exposed to the mystery substance.

The envelopes were found in the mailroom for ICE’s Enforcement and Removal Operations, on the ninth floor. Other ICE offices are located on the floor above it.

The NYPD and FDNY responded to the scene as a precaution, and the building was evacuated. There were no immediate reports of anyone feeling ill.

Mayor Eric Adams said hazmat teams were at the building as test results were still pending to determine whether the incident was a hoax or a real threat. The letters would be sent to an FBI lab in Quantico, Virginia, for additional testing.

The FBI did not state what was written on the letters that accompanied the powder. An investigation is ongoing.

The suspicious letters came on the heels of reported cases of ICE agents detaining immigrants after they leave their immigration court hearings. Advocates and lawyers accuse ICE of detaining dozens of migrants for days or weeks in tight quarters on the 10th floor. A federal judge recently ordered ICE to improve conditions and limit capacity.

“Sending threatening letters of this nature, whether real or a hoax, is a crime,” said Christopher Raia, the assistant director in charge of the FBI’s New York Field Office.