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New York City Mayor Bill de Blasio warned on Tuesday — the first day of in-person public school classes for hundreds of thousands of kids — that the Big Apple’s latest soaring COVID-19 infection rate could force the system to go all online.

With the city’s daily positive testing rate hitting 3.25 percent Monday “for the first time in months,’’ the city will be watching a rolling seven-day average of the figures and is poised to shut down on-site learning if it hits 3 percent, the mayor said.

“Obviously, everyone is concerned about’’ the latest 3.25 percent daily figure — after weeks of the rate hovering around 1 percent, Hizzoner said.

He blamed spikes in positive tests in neighborhoods in Brooklyn and Queens for the jump.

Monthly random testing of students, teachers and other school workers will start next week, de Blasio noted.

City public high schools are scheduled to begin in-person learning Thursday.

Nearly half of all city public school students have already opted to only take online classes.

The city’s principals union had asked the state Sunday to take over the Big Apple school system, alleging dangerous ineptitude by the de Blasio administration in its handling of the reopening of classes amid the coronavirus.

Gov. Andrew Cuomo doubled down Tuesday on his previous warning that the state may have to launch such a takeover.

“If those schools are not safe, I will not allow them to operate. Period,” Cuomo told reporters.

“The state can close down any school in the state of New York,” he said. “New York City, Buffalo, Long Island — you have my word as a parent, as a citizen, as your representative — if a school is not safe, I will not allow them to operate.”