Between 20 to 50 people were quarantined after an envelope with a suspicious powdery substance was opened inside a Bay Area United States Customs office Wednesday, fire officials said.

Emergency crews responded to the U.S. Customs and Border Patrol Office located at 2430 Mariner Square Loop in Alameda, California after three people fell ill, according to the Alameda Fire Department.

Alameda fire officials were called out to the office at 2:43 p.m. after an employee opened an envelope and came in contact with a powdery substance, Juan Medrano with Alameda Fire said. The employee started feeling nauseous and dizzy shortly thereafter. Fire officials established a "hot zone" in the area. After their arrival, two more people fell sick. None of the symptoms are considered life threatening, fire officials said.

Police were asking people to avoid the area due to the "hazardous material incident." Hazmat officials were also on the scene trying to determine the nature of the substance.

The employees who fell ill were being treated within the quarantined area, officials said. All three employees were feeling better later in the afternoon, officials said.

The envelope was sent to a lab for further testing.