More than 7,000 nurses at two major Big Apple hospitals went on strike early Monday, after negotiations over contracts and staffing broke down overnight.

Nurses at Mount Sinai Hospital’s main campus on Madison Avenue and three locations of Montefiore Medical Center in the Bronx staged walk-outs starting in the early morning hours, the New York State Nurses Association said.

“After bargaining late into the night at Montefiore and Mount Sinai Hospital yesterday, no tentative agreements were reached,” the union said in a statement. “Today, more than 7,000 nurses at two hospitals are on strike for fair contracts that improve patient care.”

The affected locations in the Bronx are Montefiore Moses on East 210th Street, Montefiore Weiler on Eastchester Road and Montefiore Hutch on Waters Place. 

Mount Sinai Health System criticized the nurses’ decision to strike, in a statement posted to Twitter early Monday.

“NYSNA leadership walked out of negotiations shortly after 1 a.m. ET, refusing to accept the exact same 19.1% increased wage offer agreed to by eight other hospitals, including two other Mount Sinai Health System campuses, and disregarding the governor’s solution to avoid a strike,” the statement said. 

The walkout comes just a day after a high-ranking Mt. Sinai obstetrics physician emphasized that his staff could be in dire straits if a walkout were to happen. 

“This is not a good thing for us, for the patients … We are really, really in a bad situation,” the chief doctor told his staff at the end of a call Sunday, preparing them for the possibility they will have to deliver their patients’ babies at Lenox Hill Hospital or NYU Langone, according to audio obtained by The Post.

The doctor and his team directed physicians to begin calling patients to prepare them for the possibility of a strike and warned that they may not be able to be present for delivery if they haven’t received credentials for the other hospitals.

Meanwhile, nurses at Mount Sinai Morningside and Mount Sinai West came to an agreement with management Sunday afternoon.

In a statement issued to CNN, Montefiore described the Monday walkout as “a sad day for New York City.”

“Despite Montefiore’s offer of a 19.1% compounded wage increase — the same offer agreed to at the wealthiest of our peer institutions — and a commitment to create over 170 new nursing positions … NYSNA’s leadership has decided to walk away from the bedsides of their patients,” the medical center said. 

Union President Nancy Hagans told reporters Sunday morning that “the No. 1 issue is the crisis of understaffing” that has left nurses spread thin.

The emergency room at Montefiore, where the union has 3,476 members, “is often so overcrowded that patients are admitted in beds in a hallway instead of hospital rooms,” Hagans said.

“We are here to negotiate in good faith, to make sure that the nurses have enough resources to care for the patients.”

In the Monday statement, the union urged New Yorkers to “please do not delay getting medical care, regardless of whether we are on strike.”

“Patients should seek hospital care immediately if they need it,” the statement said. “We would rather be the ones providing that care, but our bosses have pushed us to be out here instead.”

“We appreciate solidarity from our patients — but going into the hospital to get the care you need is NOT crossing our strike line. In fact, we invite you to come join us on the strike line after you’ve gotten the care you need. We are out here so we can provide better patient care to you!”

In a statement Sunday, Gov. Kathy Hochul said that the state Department of Health “will continue to enforce staffing requirements under the law at these hospitals to maintain the delivery of essential health care services to the community and protect patient health and safety.

“Likewise, the Health Department will continue to ensure that all providers are meeting the requirements of the law.”

Mayor Eric Adams said Sunday that the city is “prepared for a potential strike” but “hopeful that all parties keep working to reach a voluntary agreement.” 

He warned of “possible delayed or limited service” at affected hospitals and urged New Yorkers to call 911 only in emergencies, and to seek care elsewhere if their preferred hospital is affected.