Do not leave your house unless you are buying groceries, picking up pharmacy items, or helping sustain life, Gov. Tom Wolf told residents of Philadelphia, Montgomery, Bucks, Chester, Delaware, Monroe, and Allegheny Counties on Monday, putting them under a stay-at-home order.

With exceptions for critical errands and work designated essential, keeping the 5.5 million people in those counties at home until at least April 6 offers officials the best chance to slow the spread of the coronavirus in Pennsylvania and keep from taxing the state’s health-care system, Wolf said.

“Before we can recover, we must survive. And to do that, every one of us must do our part,” Wolf said.

His directive effectively extended to six other counties a stay-at-home order that Mayor Jim Kenney put in effect in Philadelphia on Monday morning. The city and the other counties affected by Wolf’s order — including the one that contains Pittsburgh — represent the state’s worst areas of virus spread. The governor also ordered schools statewide to stay closed for an additional two weeks.

Residents in the rest of Pennsylvania continue to be urged by officials to stay home, practice social distancing, and keep six feet away from others.

“You must stay in your homes unless not leaving your home endangers a life,” said Wolf, who spoke from his home via video Monday. “That’s what’s going to … buy us the time that we need to allow our health-care system to build the capacity they need to treat all of us.”

On Sunday, Gov. John Carney ordered Delaware residents to stay home and nonessential businesses to close starting at 8 a.m. Tuesday. New Jersey Gov. Phil Murphy put residents under the same order on Saturday.

The new restrictions came as the U.S. surgeon general warned the country Monday that “this week, it’s going to get bad,” and the World Health Organization said the spread of the virus was accelerating. The United States reported more than 100 deaths on Monday, marking the first day with a triple-digit death toll since the pandemic arrived and pushing the country’s total fatalities past 500.

Six people in Pennsylvania and 27 people in New Jersey have died of the virus; no deaths have been reported in Delaware. On Monday, Pennsylvania reported 644 cases, New Jersey 2,844, and Delaware 87.

Major U.S. airlines are drafting plans for a voluntary shutdown of virtually all domestic flights, the Wall Street Journal reported late Monday, citing as sources industry and federal officials. “No final decisions have been made by the carriers or the White House,” the Journal reported. U.S. airlines have already eliminated most international flights and are experiencing mass cancellations for domestic flights.

U.S. airlines including American Airlines, which accounts for 70% of traffic at Philadelphia International Airport, and United Airlines canceled over 40% of scheduled flights across the country Monday, according to Flightaware.com, a flight tracking site. Philadelphia International Airport saw 29% of its outbound flights canceled Monday.

Wolf said now is the time when social distancing and stay-at-home measures could help prevent the state from seeing the same disaster as Italy, where more than 6,000 people have died and nearly 65,000 have been infected as hospitals have been overcome by the pandemic.

“About every two days, we are more than doubling the number of cases of COVID-19. It’s going straight up,” Pennsylvania Health Secretary Rachel Levine said. The prevention efforts aim “to bend the curve in the number of new cases and prevent that surge.”

Because people with the virus are contagious for up to two weeks before they show symptoms, Wolf said “we have to act as if we have it” and operate under the knowledge that “by staying at home, you might be saving a life.”

Pennsylvanians under stay-at-home orders are allowed to go out for outdoor activity; medical care; grocery shopping; medicine, medical or work supplies; care for family members, dependents, vulnerable people, or pets; and work at a “life-sustaining” business or government agency.

That means no picnics, outdoor parties, play dates, or pickup basketball games. No unnecessary shopping, and no in-person socializing. Wolf said he and his wife, for instance, have not met their newborn grandson.

In another preventive measure, Kenney announced Monday that the Independence Blue Cross Broad Street Run, originally scheduled for May 3, was rescheduled for Oct. 4. The city was also preparing to turn a Center City hotel into a quarantine site for coronavirus patients experiencing homelessness. All 13 floors of the Holiday Inn Express on Walnut Street near 13th will become housing for people awaiting test results or who are being quarantined, and could also accommodate health-care workers with symptoms, sources said.

Law enforcement officers will be spreading awareness of Wolf’s stay-at-home order in the affected counties, and Philadelphia police will try to disperse groups of people but won’t make arrests or citations, city officials said. District Attorney Kevin R. Steele said Montgomery County law enforcement was prepared to enforce the directive but hoped for voluntary compliance.

New Jerseyans risk being cited and prosecuted if they do not follow Murphy’s orders to stay at home and close all nonessential businesses, top officials said Monday.

“Consider this as your final warning,” Attorney General Gurbir S. Grewal said. “Your actions are against the law in New Jersey [and] you will be held accountable.”

Meanwhile, officials in Pennsylvania and New Jersey, like those in other states, are scrambling to secure medical equipment such as ventilators, masks, and beds. Both states are considering using hotels for patients in recovery, officials said Monday, and “working on plans” to get more resources.

“We need to continue to do our job; in order to do so, we need the federal government to come in with a big bucket of money,” said Murphy, who had a private phone call with President Donald Trump on Monday and has asked for more protective equipment, assistance from the Army Corps of Engineers to build four temporary hospitals, and at least $100 billion in regional aid to share with Pennsylvania, New York and Connecticut.

Also Monday, New Jersey’s Supreme Court ordered those serving less than a one-year sentence for low-level offenses in county jails to be released temporarily on Tuesday to mitigate the spread of the coronavirus in correctional facilities. The order could mean the release of up to 1,000 people, according to the ACLU of New Jersey.

The Philadelphia District Attorney’s Office called for the state judiciary to take similar steps, saying people on bail for nonserious offenses, eligible for parole, ill or elderly, and certain others are in jail unnecessarily during the pandemic.

“Jails and prisons are landlocked cruise ships, with people in extremely close quarters and supplies such as soap and sanitation products drying up. Safely and swiftly depopulating corrections facilities is a matter of life or death for all of us,” District Attorney Larry Krasner said in a statement.

Acknowledging the restrictions — and the situation — are unlike anything most people have experienced before, Wolf, like other officials, said isolating at home was the only way to unite against the virus.

“If you are in a county under a stay-at-home order … don’t leave your home unless someone’s life depends on your leaving," Wolf said, "because ultimately, someone’s life does depend on you staying.”

Contributing to this article were staff writers Ellie Rushing, Allison Steele, Chris Brennan, Mike Newall, Rob Tornoe, Oona Goodin-Smith, and Frank Kummer, as well as Angela Couloumbis of Spotlight PA.