OLYMPIA — Continuing a drastic escalation to slow the spread of the novel coronavirus, Gov. Jay Inslee announced Friday he would mandate the closure of all Washington schools from March 17 through at least April 24.

In the same announcement, Inslee said he would extend a restriction on social gatherings of over 250 people — such as concerts and sporting events — to the entire state. And the governor said he would expand visitor restrictions placed earlier this week on nursing homes and assisted living facilities to also include adult family homes.

Inslee also said he would “restrict activities” at colleges, saying there would be no in-person courses through that date. Labs and clinics, he said, can continue if social distancing is imposed.

The measures were necessary to confront “a clear and present danger of rather epic proportions in the state Washington,” said the governor.

“I’m not sure we’re ever faced this since the 1918 Spanish flu,” said Inslee.

The move came one day after the governor said he was using an executive order to mandate K-12 school closures in King, Pierce and Snohomish counties for those same dates. At colleges, he said, dormitories, food service, research and medical clinics can remain open, too.

School districts here have begun planning for ways to get core services, such as food, to families. Meanwhile, closures spread across the country, from Oregon to Ohio to Los Angeles, as officials everywhere ramped up their efforts to slow the spread of the novel coronavirus.

Shutting schools statewide affects more than just instruction. Schools are a critical lifeline for low-income families, who rely on schools to provide free or reduced-price lunch and often other meals each day.

Across Washington state, traditional public and charter schools enroll more than 1.1 million. About 82,000 were enrolled in private schools in the 2017-2018 school year. More than half a million public-school students — about 45%, or 520,000 statewide — qualify for subsidized meals at schools, meaning many families throughout the state will struggle to feed their children during a prolonged school closure.

By the end of next week, state schools chief Chris Reykdal said he expects to compile every school district’s plan for childcare, nutrition services and graduation pathways for juniors and seniors in high school. He asked families to be patient while districts plan.

Reykdal said districts should be prioritizing childcare for health workers and first responders. Some districts with in-building preschool or early childhood programs are already set up to do this, but others will have to seek outside providers, he said. He challenged parents to look beyond their schools for assistance. “High school and middle school students will be at home,” said Reykdal. “We’re talking about a small subset … of students who can’t find that support.”

Another 14% of K-12 students in Washington — nearly 170,000 — have a disability and receive special education services in schools. Under federal law, students with disabilities are guaranteed a right to “free and appropriate” public education. But if school closures completely halt academic offerings for everyone, guidance from the U.S. Department of Education says schools do not have to provide services to students with disabilities. Conversely, if schools decide to offer online learning or any other service during closures, they must ensure that students with disabilities can access it.

Several school districts that have already closed are looking for ways to get meals to students in need, such as bussing meals to neighborhoods where lots of students live. It may be a challenge to scale up such methods statewide.

Already, Washington received a waiver from the federal government to make it easier to provide meals to students and their families. And the U.S. Department of Education said it would consider temporarily waiving requirements to administer standardized tests to students in districts affected by closures.

As of Friday, it remained unclear exactly whether or how hourly and part-time workers in schools — including bus drivers, paraeducators, substitute teachers and other staff — would draw a paycheck during a six-week school closure. A spokesman with the state’s Employment Security Department said part-time workers, provided they’re actually laid off from their jobs, are typically eligible for unemployment benefits if they have worked 680 hours or more in the previous year. Workers must wait a week from the date of unemployment to receive those benefits.

Standardized tests, which typically start each spring, likely will be suspended.

Very little is known about COVID-19 transmission and infection in children, which complicates what we know about whether closing schools will work as a mitigation technique. Emerging research hints that only long-term closures — those over eight weeks — will put a dent in the virus’s spread.

Inslee’s Friday announcement followed new recommendations from the Centers for Disease and Control and Prevention that suggest short-term school closures may have no impact on the magnitude or trajectory of spread of the coronavirus. Closing school for eight to 20 weeks may help curb the virus, though other strategies — such as encouraging frequent hand-washing — are likely more effective, the CDC guidance says.

Under state law, public school districts must offer a minimum average of 1,080 instructional hours to high school students and 1,000 hours to all other grades. The state education department will waive days that school districts can’t make up past June 19.

A bill the state Legislature passed Thursday permits the state board of education to grant flexibility on credit requirements for high-school students who were on track to graduate before their schools closed.