San Francisco’s surge in coronavirus cases placed the city back in the state’s most restrictive “purple tier,” signaling new rules starting Monday, Mayor London Breed announced on Twitter Saturday.

A limited stay-at-home order will mean all nonessential indoor businesses will close and members from different households will not be permitted to gather between 10 p.m. and 5 a.m. until Dec. 21.

Outdoor dining, indoor retail, indoor personal services and outdoor fitness will remain open. Outdoor recreation, such as zoos, batting cages and mini golf may remain open.

Indoor activities, including worship, must cease, with exceptions. Funerals are allowed indoors with up to 12 people and outdoor religious services are allowed with up to 200 people.

The city also issued a travel advisory, warning residents not to travel outside the county.

“I don’t know how to be more clear–this is the most dangerous time we’ve faced during this pandemic. Do not travel or gather with others,” Breed tweeted.

“This is the most aggressive surge SF has seen to date. We’re currently averaging 118 new cases per day compared to 73 per day in the first week of November,” she said. “For the week of November 16th, we had 768 diagnosed cases compared to 217 diagnosed cases the week of October 12th.”

California Gov. Gavin Newsom imposed an overnight curfew through December on Nov. 19 for 41 counties in the “purple” tier, but that did not apply to San Francisco at the time. Purple, or Tier 1, is the most severe level, indicating that the virus is widespread in an area, with more than seven cases per 100,000 residents.

On Friday, Los Angeles County issued a safer-at-home order from Nov. 30 to Dec. 20 that included stricter limits on going out and gatherings.

Under the new order, residents are being asked to stay home “as much as possible” and to wear a face covering outside.

Public and private gatherings with anyone outside one’s household are prohibited. Religious services and protests are exempted. Occupancy limits for retail businesses will be capped at 35%, malls at 20% and 50% for fitness centers.

Health officials raised concerns about a spike in transmissions before the Thanksgiving holiday and the upcoming holidays next month. Nearly 90,000 are currently hospitalized with the virus in the U.S.

The Centers for Disease Control urged Americans to forego travel over the holiday, but the Transportation and Security Administration screened over 3 million people the weekend before Thanksgiving, the highest number on any weekend since March.