NEW YORK (AP) — As schools across the U.S. shut down in hopes of helping to fight the coronavirus, New York City officials are arguing just the opposite: They're keeping the nation's largest school system open to ensure that health and emergency workers aren't tied down with kids at home.

But teachers, many parents and some health experts say the city is making a grave mistake by continuing to call more than 1.1 million children to public schools even as it calls for “social distancing” elsewhere to stem the virus' spread.

While many families elsewhere in the country spent Saturday making hasty plans for an unexpected school shutdown, New Yorkers debated the city's decision.

"You're not going to have a functioning health care system if the folks in the medical field, the doctors, the nurses, the techs, everyone has to stay home with their kids,” Mayor Bill de Blasio said on MSNBC.

Parent Anna Gold didn't see it his way.

“It would be a hardship if they closed the schools, but I think it's a necessary one we need to take in the space of this emergency,” said Anna Gold, who pulled her third-grader and kindergartner out of public schools in Brooklyn on Friday and plans to keep them home next week.

Another parent, Dori Kleinman, said she wishes the mayor would allow individual schools to make a decision about whether to close.

“I don't want my children at risk,” she said.

New York City became a big outlier as other major U.S. cities, including Los Angeles and Boston, and several states decided to shutter schools for a week or more.

New York health care workers' unions said the city shouldn't close schools without a plan to care for the children of those staffing hospital wards. The unions and city officials fear that even New York's massive health care system could be quickly overwhelmed by a surge in serious cases of COVID-19, the disease caused by the new coronavirus.

“If it’s apparent it’s the safe thing, then it must be done, but it’s going to have a big impact on nurses,” said Eileen Toback, executive director of the New York Professional Nurses Union, which represents nurses at Manhattan’s Lenox Hill Hospital. “They’re on the front lines. They need to be here in shifts. They’re single mothers or single fathers sometimes, so they don’t have many backups, and the hospital is 24/7.”

De Blasio, a Democrat, has not ruled out closing schools eventually and said city officials would continue a day-by-day examination. But he has noted that the federal Centers for Disease Control and Prevention say that while there can be reasons to shut schools, it's not clear that closures will make more difference than other measures, such as hand-washing and isolating the sick.

But Dr. Dena Grayson, a researcher and infectious disease expert who works in the private sector, called de Blasio's decision so far to keep schools open “incredibly foolish.”

“The virus will spread like wildfire among the children. They get infected, and they can spread that virus easily to older people who are at a much higher risk," she said.

The city has confirmed coronavirus cases in at least two public school students and at least one teacher. Their schools have been closed for cleaning but are expected to reopen.

For most people, the virus causes only mild or moderate symptoms, such as fever and cough. For some, especially older adults and people with existing health problems, it can cause more severe illness, including pneumonia. The vast majority of people recover, but the outbreak has caused more than 5,000 deaths worldwide.

Teachers' unions are pressing de Blasio to close the schools, saying they’re worried for their students’ families, their own and New Yorkers at large.

“To have 1.1 million students and countless employees crisscrossing the city, it feels to me beyond irresponsible,” says Derek Stampone, who teaches physics and computer science at a Manhattan high school where only about 2/3 of students showed up Friday, a dropoff echoed in the system as a whole. Stampone found himself spending much of Friday’s classes talking about the virus and such prevention tips as hand-washing.

“I can see the anxiety in the room,” he said.

So did social studies teacher Elise Ritter, who works at a different Manhattan high school that happens to focus on emergency management.

The students who did attend, she said, were “really looking around and saying, ‘Why are we still here?’” Many live with grandparents and worry about them contracting the virus, she said.

Teachers suggest the city could find ways to provide child care for health care workers — and supply food to the hundreds of thousands of poor students who depend on school meals — without keeping the entire school system open.

De Blasio has said that any alternative would recreate the problem that closing schools would seek to solve: People congregating.

Gov. Andrew Cuomo, a Democrat, said school closings remain “purely a local decision” unless a student tests positive, in which case a school must be closed for cleaning.

“The closing of schools is a significant trade-off of benefits and burdens,” he said Saturday in a conference call with reporters. "If you close the schools, there are people who will not show up for work the next day. The public education system is also a day care, in many ways.”

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Associated Press reporters Adam Geller and Vanessa Alvarez contributed to this report. The Associated Press receives support for health and science coverage from the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.