Vallejo police say they responded to the shooting in the 500 block of Fairgrounds Drive around 5:25 p.m.
When officers arrived they found a person suffering from at least one gunshot wound.
That person, who has not yet been identified, was later pronounced dead at the scene, police said.
"The other party involved in the shooting remained on-site and was determined to be an off-duty Richmond Police Officer," Vallejo PD said in a statement.
Further details are not available at this time.
Stay with ABC7 News for the latest details on this developing story.