Just after 3:05 p.m., Alameda County's hazardous materials team responded to the Union City Police Department in the 34000 block of Niles-Alvarado Road, county fire spokeswoman Aisha Knowles said.
In Berkeley, another package carrying an unknown substance was reported in the building at 2100 Martin Luther King Jr. Way at 2:15 p.m., Berkeley police said.
The department's building was partially evacuated, a police officer said.
Knowles said county fire crews were working with Berkeley firefighters to identify the substance.
Earlier, the county hazmat team and firefighters responded to the San Leandro police station at 901 E. 14th St. after an unknown substance was reported there around 1:45 p.m., Knowles said.
The substance has since been tested and deemed harmless, she said.
This morning a powdery substance was also delivered to the Hayward Police Department.
Tests this afternoon revealed the substance in Hayward was not anthrax, according to Hayward fire officials.
Knowles did not immediately know if the four incidents are connected.
Berkeley police said they were in contact with the Hayward and San Leandro police departments to determine if there is a link.