The declaration means that the California Department of Public Health can immediately purchase and distribute vaccines to affected communities, CBS News reported.
To date, 576 cases of hepatitis A have been reported statewide, but a large majority of cases of have occurred in San Diego. Earlier this month, San Diego County officials declared a public health emergency in response to the outbreak that has killed 16 people and hospitalized 300 more since last November.
Los Angeles and Santa Cruz counties are also affected.
It's the largest outbreak of the liver disease in the United States transmitted from person to person -- rather than through contaminated food -- since the hepatitis A vaccine became available in 1996, CBS News reported.
Most patients are homeless or drug users, but some are also employees at a health care facility working with those patients, according to a health official.