San Francisco Mayor London Breed (C) speaks during a press conference as San Francisco police chief William Scott (L) and San Francisco Department of Public Health director Dr. Grant Colfax (R) look on at San Francisco City Hall on March 16, 2020 in San Francisco, California.

San Francisco Mayor London Breed announced Monday that health officials are extending the city's stay-at-home order through May.

Six counties in Northern California, including San Francisco, plus the city of Berkeley, will introduce extended stay-at-home orders this week, according to a joint statement released by county health officials. The extended orders will also include the lifting of certain restrictions.

"We do expect some lower-risk activities to be allowed to resume soon, but for the safety of you and those around you we must build on the progress we've made," Breed said in a tweet Monday announcing the order's extension.

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She said that the city does not want to relax restrictions too early in the event there's a spike in cases and even stricter restrictions on city residents are required.

San Francisco banned gatherings of more than 1,000 people on March 11 and joined five other Bay Area counties on March 16 as the first region in the U.S. to order residents to "shelter in place," that is, avoid leaving their homes except for essential business such as grocery shopping and medical visits. On March 19, the entire state of California followed suit.

Infectious disease experts say that the region's early steps, including ordering people to avoid crowds and shelter in place, may have slowed the trajectory of the virus. But experts say it remains critically important that residents continue to heed the advice of public health officials and stay home.