Life came to a grinding halt for millions of San Francisco Bay Area residents as the most stringent isolation orders in the country took effect Tuesday.

To stem the spread of the new coronavirus, roughly 7 million people in seven counties were instructed to “shelter in place” and were prohibited from leaving their homes except for “essential” activities such as purchasing food, medicine and other necessities. Most businesses closed, with the exception of grocery stores, pharmacies, restaurants (for takeout and delivery only), hospitals, gas stations, banks and a handful of others.

The county orders, which have the force of law behind them, will last until April 7, although health officials could extend or shorten that deadline. Disobeying the orders could be a misdemeanor punishable by fine or imprisonment.

For many people in the famously unaffordable Bay Area, the orders could well mean lost wages and jobs, as customers disappear and businesses struggle to pay their bills.

“It’s unprecedented in modern times to have this level of quarantine-like measures,” said Jeffrey Schlegelmilch, deputy director of the National Center for Disaster Preparedness at Columbia University in New York City.

The Bay Area orders, which affect San Francisco, Santa Clara, San Mateo, Marin, Alameda, Contra Costa and Santa Cruz counties, have sown confusion, in part because cities, counties and states across the country are creating different, sometimes conflicting rules for their residents. Just one day before the shelter-in-place orders were announced, Gov. Gavin Newsom called on all California residents 65 and older to stay home, then expanded his orders after the Bay Area news broke.

On Tuesday, Sonoma, San Benito and Monterey counties joined the Bay Area counties in ordering their residents to stay at home.

Sacramento County issued a similar directive, although it stopped short of legally ordering people to shelter in place. Ventura County directed older residents to shelter in place.

Other places around the country are expected to follow the Bay Area’s example, including New York City, where Mayor Bill de Blasio told residents Tuesday to expect a shelter-in-place order within the next 48 hours.

Q: Why is this happening in the Bay Area?

These seven counties have more than 350 confirmed cases of COVID-19, including at least five deaths. But because testing has been so limited, the actual number of residents infected with the novel coronavirus is likely far higher than the official count.

“We have been operating under a veil of ignorance because we do not have a sense of the truth,” Schlegelmilch said. “Rather than having more specific measures aimed at containment, we have to have much more aggressive and widespread social distancing measures over the entire population to prevent this from completely overwhelming our health care system.”

The Bay Area is already seeing community spread of COVID-19, and the number of new cases is growing daily. In San Mateo County, for example, officials announced Tuesday that cases had jumped from 42 to 64 overnight.

“The infection rates in the six most populous counties of the Bay Area and the City of Berkeley suggest that the situation is critical and will worsen quickly, especially without rigorous intervention,” Santa Clara County wrote in an FAQ for residents.

The health care system is already overwhelmed in some areas, the county said: “The sooner these extreme measures are taken, the more effective they are because of how the virus spreads.”

Q: Are such extreme measures really necessary?

While the new orders may seem draconian, public health experts say they are good policy.

The Bay Area counties, like the rest of the country, don’t know how pervasive the virus is. And while a trove of studies prove that social distancing helps stem the spread of coronavirus, there is less agreement about what exactly that looks like. For instance, is it necessary to prohibit gatherings of more than five people? Or is more than 50 enough?

It’s better to err on the side of caution, said Dr. Ashish Jha, a professor of global health at Harvard University. “The cost of overreacting is that there’s an economic cost and a social cost,” he said. “But the cost of underreacting is a lot of people dying unnecessarily.”

Even though Americans had been warned to stay home and avoid big public gatherings, photos circulating on social media over the weekend showed that many people were continuing to carry on life as usual, Jha said, such as gathering at bars, meeting for brunch and attending St. Patrick’s Day parades.

“We are late in the game and we need to act aggressively,” Jha said.

Q: Should these decisions be made at the regional level?

Public health authorities in cities, counties and states often have more extensive powers than federal officials to order quarantines during emergencies, said Schlegelmilch of Columbia. That’s because their authority was conferred in the days of smallpox and yellow fever, he explained.

Failure to comply with the new Bay Area orders, for example, may be punishable by a fine or imprisonment, according to the city of San Francisco.

But when President Donald Trump on Monday warned Americans not to gather in groups of 10 or more, and to work from home if possible, those were suggestions rather than legal orders.

Dr. Richard Waldhorn, a professor of medicine at Georgetown University, said a regional approach makes sense, especially in a large and heterogeneous state like California.

“The deserts probably don’t need as extreme measures as the heavily populated Bay Area,” he said.

And rural areas of the state may be reluctant to order residents to stay in their homes, said Dr. George Rutherford, a professor of epidemiology at the University of California-San Francisco.

“We have a huge agricultural workforce that has to get the crops planted so we have food later in the year. If you miss that, there are big consequences of that,” he said.

Q: What kind of economic help is available to people affected by the orders?

There’s no question that millions of Californians will take a financial hit from the crisis.

“Every time you’re implementing measures to prevent a public health disaster, you’re unintentionally creating another disaster” because of economic slowdowns and wage losses among people who are paid hourly or can’t work remotely, Schlegelmilch said.

Leaders promise that help will be available at the federal, state and local levels.

The Trump administration proposed a $1 trillion economic stimulus plan Tuesday, including sending cash payments to Americans and delaying tax payments for 90 days, which requires congressional approval.

California was the first state to get the federal Small Business Administration to offer loans to both for-profit and nonprofit businesses hurting because of the outbreak. Loans of up to $2 million are available.

California legislators on Monday night passed a $1.1 billion emergency response package that will include assistance for individuals, nonprofit organizations and small businesses, but the exact details haven’t been hammered out yet. Lawmakers then suspended the legislature for the first time in 158 years, and won’t reconvene until April 13 or later.

The state is also encouraging workers to file disability insurance claims if they’re sick, or apply for paid family leave if they are quarantined or caring for sick family members. Newsom waived the one-week waiting period to file for unemployment and disability insurance. Workers may also be eligible for workers’ compensation benefits if they can’t do their jobs because of the virus.

While tenants still have to pay rent, Newsom authorized local governments to stop evictions, slow foreclosures and stop cutting off utilities during the outbreak. San Francisco, San Jose, Oakland and Los Angeles are among the localities taking steps to halt evictions.

There are more local relief plans in the works. The city of San Francisco announced a $10 million plan to provide an additional five days of sick leave to workers who are home sick or caring for family members.

Q: Who can go into work?

Not a lot of people.

In the affected counties, people who can work from home are required to do so. And those who staff “essential” services, such as health care, municipal sanitation services, law enforcement and jails, are still on the job.

Each county has defined what’s essential in their jurisdiction. For instance, San Mateo County says fishermen can work, and San Francisco has special instructions about nannies.

Anyone working in gas stations, pharmacies, grocery stores, hardware stores, banks and laundromats, and people like plumbers and veterinarians, also are allowed to work.

There are some other circumstances in which workers are allowed to do their jobs in person. People making and delivering food can, but people serving it cannot. Drivers for ride-hailing companies and operators of public transit can still work, but those services should be used only for “essential” travel.

But such stringent orders cannot last forever, even with government aid.

“How long can that go on before you start to see detrimental effects on people?” asked Schlegelmilch of Columbia.