The order says residents must stay inside and venture out only for necessities for three weeks starting Tuesday in a desperate attempt by officials to curb the spread of the novel coronavirus.

“I know today’s order is a radical step. It has to be. We need to act now, all of us, to protect the public health,” said Dr. Grant Colfax, director of the San Francisco Department of Public Health.

If affects the counties of San Francisco, Marin, Santa Clara, Santa Cruz, San Mateo, Contra Costa and Alameda, which includes the cities of Berkeley and Oakland.

“History will not forgive us for waiting an hour more,” said San Jose Mayor Sam Liccardo, whose city is the most populous in the Bay Area and the epicenter of the area’s outbreak. “This is our generation’s great test, our moment to stand tougher as a community. Amid our collective fears, we will find our uncommon courage.”