According to an announcement released by the city mayor London Breed, over the last three weeks, all Bay Area counties have seen at least a doubling of new Covid-19 cases, causing concern that unvaccinated people are more at risk than ever, reports Xinhua news agency.
The Delta variant spreads more easily than the original virus and poses new risks to communities in San Francisco, the announcement said.
"Vaccinating as many people as possible, as soon as possible, is our best defence against Covid-19, the delta variant, and the harm it can do to our communities," said Breed.
"In particular, the Black community has the lowest vaccination rate compared to the citywide rate."
San Francisco's response to the pandemic has resulted in low case rates and hospitalizations, and relatively high vaccination rates, with 83 per cent of the eligible population with at least one dose and 76 per cent of the eligible population fully vaccinated as of July 13.
Over the week ending July 7, for which there is full data, the city's average daily new cases have increased four-fold to 42 new cases per day from a low of 9.9 cases per day on June 19.
Forward-looking data through July 12 indicates that new cases will increase to at least 73 cases per day, a seven-fold increase since June 19.