White powder was found at the San Mateo County building in Redwood City, Calif., according to a report on Thursday.
A hazmat team was deployed to the building to investigate the matter, reported KTVU-TV.
The powder was found inside a letter, the station said.
It is unclear if any of the workers were exposed to the substance.
ABC-7 reported that the officials in the building, located at 450 block of County Center Road, issued a partial evacuation. The second floor was cleared.
The package containing the white substance apparently came in overnight and an employee found it Thursday morning.
Story is developing; check back for updates.
