A surge in coronavirus cases will put San Francisco under a curfew beginning on Monday and trigger other restrictions related to the virus, the city announced.
The curfew requires non-essential businesses to close and prohibits members of different households from gathering between 10 pm and 5 am until December 21, Mayor London Breed said Saturday.
San Mateo county outside San Francisco will also be subject to the same rules after the state of California classified both under its most restrictive tier of locations based on the spread of the virus.
In addition to the curfew, certain indoor businesses will be required to either close or reduce capacity beginning on Sunday at noon, Breed said.
"I don't know how to be more clear -- this is the most dangerous time we've faced during this pandemic," Breed said on Twitter.
"Do not travel or gather with others. We have to get this under control now and we can't afford to let things continue at this rate."
On Friday, a temporary ban on gatherings of people from different households, with religious services and protests exempt, was announced for California's largest city, Los Angeles.
That order affecting the United States' second-largest city will take effect Monday and last at least three weeks, until December 20, Los Angeles county's public health department said.
California imposed a night-time curfew across much of the state a week ago, but San Francisco was not affected because it was not at the time classified among the state's most restrictive tier of locations.
The United States on Friday topped 13 million Covid-19 cases -- the world's highest -- and President-elect Joe Biden has warned of difficult weeks ahead before vaccines become widely available.