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.

Police evacuated 26 Federal Plaza in Manhattan after envelopes containing white powder were discovered Thursday afternoon, officials said.