New York City nurses on strike restarted contract talks Friday with another major hospital system as the walkout entered its fifth day, according to the New York State Nurses Association.

The union said its bargaining team resumed meetings with counterparts at the three Mount Sinai hospitals at the request of a mediator.

Brendan Carr, CEO of the Manhattan-based health care provider, said administrators were working to bring the medical facilities to full capacity while negotiations continued toward a deal to end the city’s biggest strike of its kind in decades.

Carr also said Mount Sinai has extended its contracts to retain thousands of temporary nurses to fill shifts. He said the hospital system was also bringing on more specialized staffers to help bring surgical volumes back to normal.

Nurses met Thursday night with NewYork-Presbyterian officials and a federal mediator in what the report described as the first negotiations since about 15,000 nurses walked off the job Monday. The hourslong meeting ran past midnight and ended with very little progress made, according to the union.

The hospital said in a statement that the discussions focused on addressing the union’s concerns about staffing levels, but it said it still views the union’s proposals as “unreasonable.” The union said it put forward revised proposals that hospital officials rejected without offering a counterproposal.

The two sides said there were no further plans to meet. NewYork-Presbyterian said in a statement, “While we continue to be far apart, we are committed to bargaining in good faith,” and it said, “We are committed to safe staffing and have the best staffing ratios in the city.”

Union negotiations were still not under way with Montefiore, the third major hospital system affected by the walkout. The union said it had expected to meet with officials from the Bronx-based provider Friday, but the hospital disputed that claim, saying a meeting was never planned.

“NYSNA nurses respect the mediators and are ready and willing to come to the bargaining table when they call,” Nancy Hagans, the nurses’ union president, said in a statement. She urged hospital executives to do the same.

Each medical center was negotiating with the union independently, and not every hospital run by the three health care systems was affected by the strike, the report said. The affected hospitals said their operations have been running smoothly since they hired thousands of temporary nurses to keep emergency rooms and other facilities open during the walkout.

Dr. Philip Ozuah, president of Montefiore Einstein in the Bronx, praised those still on the job. In a letter to staff, Ozuah wrote, “Another day, another miracle,” and said, “Many thanks to our amazing teams, our most complex and exacting mission continues…providing life-saving care.”