(CNN) Los Angeles County, the nation's most populous county, will reinstate its mask mandate starting 11:59 p.m. Saturday night amid a rise in coronavirus cases and hospitalizations.
The order will require masking indoors regardless of vaccination status, Los Angeles County Health Officer Dr. Muntu Davis said in a news conference Thursday.
"We share our deepest condolences with those of you who have lost friends, loved ones, and family during this difficult time," Davis said in a news release from county health officials. "We expect to keep masking requirements in place until we begin to see improvements in our community transmission of COVID-19. But waiting for us to be at high community transmission level before making a change would be too late."
According to the news release, there were 210 new coronavirus cases reported June 15. On Thursday, more than 1,500 were reported, the highest total of new cases since mid-March, officials said.
The daily test positivity rate in Los Angeles County has risen to 3.7%, from around 0.5% on June 15, the news release said.
About 4 million county residents are not vaccinated, officials said.
Los Angeles County has reported a total of 24,566 coronavirus deaths and 1,262,578 cases.
The Census Bureau estimates that as of July 2019, 10,000,000 people lived in the county.
People throughout the San Francisco Bay Area should wear face coverings in indoor public places regardless of vaccination status, health officials recommended Friday.
The Bay Area recommendation covers nearly 7 million residents living in San Francisco, Santa Clara, Alameda, Contra Costa, Marin, San Mateo and Sonoma counties as well as the City of Berkeley. Combined with a similar recommendation in Sacramento and Yolo counties and the mask mandate in Los Angeles, almost half of California's 40 million residents are advised to wear a face covering while in indoor public spaces.
San Francisco -- which has one of the highest vaccination rates in the state with 83% of residents inoculated with at least one dose -- has seen an eightfold increase in daily coronavirus cases, due in part to the highly contagious Delta variant.
"The Delta variant is spreading quickly, and everyone should take action to protect themselves and others against this potentially deadly virus," said Alameda County Health Officer Dr. Nicholas Moss.
Businesses in the region are being urged to implement universal masking requirements to provide better protection to their employees and customers, according to a joint news release sent on behalf of the Bay Area counties.
Health officers expect to keep the recommendation in place for weeks, but will reevaluate when new data is available.