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Over 4 million New Yorkers — or 50 percent of the city’s population — will get the coronavirus, Mayor Bill de Blasio warned Wednesday.

“It’s a fair bet to say that half of all New Yorkers and maybe more than half will end up contracting this disease,” de Blasio said at a City Hall press briefing about the outbreak as the Big Apple’s positive cases approached 18,000 with nearly 200 deaths.

“That’s worrisome, very deeply worrisome,” Hizzoner added.

His health commissioner, Dr. Oxiris Barbot, said the percentage could be even worse by the fall.

“We think 50 percent by the end of this epidemic, this pandemic, so by the time September rolls around, likely 50 percent, but it could also be much higher,” Barbot said at the briefing.

De Blasio added that there’s no certain patient zero for the metropolis, even though officials had previously identified a Manhattan health care worker who’d returned from Iran as the first case in early March.

“We don’t even know truly when it first asserted here in the city,” de Blasio admitted.

He reminded New Yorkers that 80 percent of people who contract the disease will have mild symptoms.

Barbot said there are currently “tens of thousands of New Yorkers” who’ve already contracted COVID-19 or been exposed to it.

“That’s why it’s so important for people to stay home,” she said.

“We don’t want all those people to be seeking health care at the same time,” she said.

The city’s hospital system is nearing its breaking point.

The shortage of safety gear at Mount Sinai West in Manhattan is so dire that desperate nurses have resorted to wearing trash bags — and some blame the situation for the coronavirus death of a beloved colleague.