Employees inside the U.S. Customs and Border Protection office in Alameda, Calif., were quarantined Wednesday after a worker fell ill after opening a suspicious envelope.

Emergency crews quarantined about 20 employees who were in the vicinity of the envelope, KTVU.com reported.

Initial reports cited the presence of a powdery substance inside the envelope. A responding Hazmat team did not find any evidence of the substance.

The incident occurred at about 2:43 p.m. local time. Two other employees also suffered a bad reaction and were treated at the scene.

The quarantine was lifted around 3:30 p.m, KTVU reported.

CBP officials said it was unknown whether the employee's illness was caused by the envelope in question.