Six Bay Area counties ordered a “shelter in place” for all residents Monday in an attempt to stop the spread of the novel coronavirus. Only essential businesses, like grocery stores or pharmacies, were allowed to remain open.

The orders affect San Francisco, Santa Clara, San Mateo, Marin, Contra Costa and Alameda counties, which hold a combined population of more than 6.7 million. The shelter in place began Tuesday at 12:01 a.m. and is to remain in effect until at least April 7.

The wording “shelter in place” is one step below a full lockdown of the counties, in which people would not be allowed to leave their homes without express permission. Violation of the directive is punishable by a fine or jail time, but most local authorities have said they would not “rush to enforce” the order residents adjust.

Public transportation in San Francisco continued to run for “essential” travel, and its international airport remains open.

“We were seeing a tipping point here in Santa Clara County with exponential growth of our cases,” Dr. Sara Cody, a health officer for the county, said during a news conference Monday. Santa Clara had 138 reported cases of COVID-19 on Monday, a large jump from 66 cases on Friday.

“Over the weekend, I had a discussion with fellow health officers in the Bay Area and we realized that we are one region, and that what’s happening in Santa Clara County today will soon be happening in the adjacent jurisdictions,” Cody said. “We decided collectively we need to take swift action as soon as possible to prevent further spread.”

She added, “These orders were crafted with great thought and with great care. They were also crafted very, very quickly.”

Other cities have been considering issuing a similar order.

New York City Mayor Bill de Blasio said Tuesday he was “absolutely considering” a shelter in place of New York.