Mayor de Blasio admitted Friday his administration has been learning on the fly as it combats the ever-growing coronavirus pandemic — and warned that the Big Apple’s overloaded hospitals could collapse under the weight of the crisis by April 5.

“After next Sunday — April 5th is when I get very, very worried about everything we’re going to need. The people power we’re going to need, the equipment, the supplies, obviously the ventilators,” the city’s embattled chief executive acknowledged during a City Hall press conference, calling the date a “crucial demarcation line.”

“That is a decisive moment for the city of New York,” he added, renewing his call for additional federal support for city hospitals.

His bombshell warning came just hours after he admitted in a radio interview that his slow response throughout could be attributed to he and his top aides struggling to get their hands around the spiraling crisis.

“You were reluctant at first to cancel school and Broadway and the St. Patrick’s Day Parade because of the economic pain. Was that balance a learning curve for you?” WNYC’s Brian Lehrer asked.

“The whole godforsaken experience has been a learning curve. None of us have ever been through anything like this,” de Blasio said, comparing the crisis to the Great Depression and World War II.

And for the first time, he promised the public some introspection about his much-criticized response to the COVID-19 outbreak.

“When we’re sure this crisis is over, we all have to assess what it means for the future, but right now we gotta survive,” de Blasio said.

The disease’s toll on New York stood at 26,697 positive cases and 450 deaths as of Friday evening.

City lawmakers, health experts and even his own staff have been deeply frustrated and oft-infuriated by de Blasio’s foot-dragging as the deadly disease began to spread across the five boroughs.

Hizzoner repeatedly dawdled on key decisions until Gov. ­Cuomo forced his hand.

The three-term governor made the decisions to shut down Broadway, cancel the St. Patrick’s Day Parade and struck a deal with key unions that effectively forced de Blasio to shut down the city’s massive public school system.

But de Blasio defended his reluctance, saying the pandemic was unprecedented.

“Nothing, I think, could prepare any of us for the speed and this thing has been so fast. March 1st, it was, I think, we had one case. It’s just breathtaking, so I think we’re learning in real time,” he said.

As de Blasio struggled to make decisions, his micromanaging tendencies left his top advisers at the Department of Health and Mental Hygiene frustrated and pushed his City Hall staff nearly to the breaking point, nearly a dozen sources told The Post over the course of a week.

Critics charge de Blasio’s pattern of micromanaging subordinates and his struggles to make key decisions have continued.

For instance, City Hall was ordered by Cuomo to produce a plan that would reduce crowding on sidewalks by closing down some city streets to vehicular ­traffic.

De Blasio responded with a small-bore pilot program that started Friday and was supposed to close up to two thoroughfares in each borough to make more room for pedestrians. As of late Friday, only four streets had been selected — and none were on Staten Island.

City Hall again frustrated the City Council and officials on Staten Island when the Department of Education decided to shutter the child-care center at PS/IS 861 in Graniteville for emergency responders, beginning Monday.

“On top of the stress these men and women face as part of their life-saving work, they are now being asked to search for new child care so they can continue to serve us,” read a letter signed by Council Speaker Corey Johnson, Public Advocate Jumaane Williams, Staten Island Borough President James Oddo and Staten Island Councilwoman Debby Rose.

“It is cruel, and they deserve better from our city,” Johnson added.

The DOE said low attendance drove the decision and that parents would get other options.