Initial testing of the white powder found in envelopes in a mailroom at a federal building in lower Manhattan reveals a substance similar to Boric acid, according to a senior official familiar with the matter.

A New York City building housing an Immigration and Customs Enforcement facility was evacuated after unknown white powder in multiple envelopes was found at the complex, authorities announced on Thursday.

The building at 26 Federal Plaza in Lower Manhattan was evacuated on Thursday afternoon following reports of a suspicious white powder.