New York’s powerful teachers union and top city lawmakers demanded on Friday that Mayor Bill de Blasio close the city’s massive public-school system, saying the coronavirus crisis has made staying open untenable.

The statements from the United Federation of Teachers and a dozen City Council members — including Speaker Corey Johnson — ramped up the pressure on de Blasio, who has resisted similar calls for days.

“We understand the immense disruption this will create for our families,” UFT President Michael Mulgrew said. “But right now, more than a million students and staff crisscross the city every day on their way to schools, putting themselves and others at risk of exposure and increasing the likelihood of bringing exposure into their homes and communities.”

He said he made his case directly to de Blasio in an hourlong talk, but Hizzoner held firm.

Mulgrew’s statement came hours after Johnson publicly called for closing the schools.

“I think it is appropriate at this time that we — instead of doing this in a piecemeal way — that we close schools temporarily,” he told NY1 in an interview.

Parents took matters into their own hands. Only 68 percent of students showed up to school on Friday, down from 85 percent on Thursday, attendance data showed.

At Wagner HS on Staten Island, only 1,000 of the school’s 4,000 students showed up for class.

“Sometimes you can’t wait for other people to make decisions,” one Brooklyn parent said, explaining why she kept her son home from elementary school. “You have to make them for yourself.”

Many teachers also stayed away from school on Friday out of coronavirus fears, union sources said.

At City Hall late Friday, de Blasio unveiled measures to reduce the risk of infection among students — including serving breakfast and lunch in classrooms — but stood by his decision to keep schools open.

“I understand the anxieties right now; I also understand that many, many parents want us to keep school open — depend on it, need it, don’t have an option,” he said.

De Blasio found an unlikely ally on the issue — Gov. Andrew Cuomo.

“To do mass closings of schools is not without consequence,” Cuomo, a frequent rival of the mayor’s, said in New Rochelle on Friday.

“You close schools, now what do you do with those children who are home all day? You close schools, you now have parents who can’t go to work, you have parents who are working in health-care facilities who can’t go to work, so it’s not that easy.”

There are 1.1 million students in New York City’s public schools, half of whom depend on schools for free or reduced-priced meals.

In other developments Friday:

The state reported the number of coronavirus cases rose from 325 to 421, with 154 in New York City.

Nassau County officials declared a state of emergency.

Cuomo warned that the state’s hospital system could be overwhelmed by coronavirus.

Other major school systems, including in Los Angeles, San Francisco, Chicago and Philadelphia, closed or planned to next week.

The Diocese of Brooklyn said it would close its schools in Brooklyn and Queens on Monday. The Archdiocese of New York is closing its Manhattan, Bronx and Staten Island schools.

The city’s largest charter-school operator, Success Academy said it’s moving classes online.