Newsom's proclamation came nine days after the World Health Organisation (WHO) declared a global health emergency, the agency's highest level of alert, over the rapidly spreading viral disease.
Around 70 countries where monkeypox is not already considered endemic have reported outbreaks, with global cases surpassing 22,100, according to a Reuters tally published on Monday. A WHO report from July 22 said only five monkeypox deaths had been reported worldwide, all of them in Africa.
To expand inoculation against the disease, California's proclamation enables emergency medical services personnel to administer federally approved vaccines, similar to the statutory authority recently enacted for pharmacists to give vaccines.
The state's monkeypox response builds on programs developed during the COVID-19 pandemic, the governor's office said in a statement announcing the declaration.
Last month, California public health leaders urged the federal government to make more vaccine doses available to the state as quickly as possible, and 25,000 does have so far been administered in California.
New York Governor Kathy Hochul declared a monkeypox emergency last week in her state, which accounts for one in four US cases documented to date.