By delaying some nonemergency pediatric surgeries, hospitals are trying to free inpatient beds to accommodate an unexpected rise in children suffering from common viruses, especially respiratory syncytial virus, or RSV.

“I think we’re in uncharted territory,” said Dr. Paul Biddinger, chief preparedness and continuity officer for Mass General Brigham, at a news briefing on Thursday.

Hospital executives said pediatric intensive care unit beds at Massachusetts General for Children were operating at 150 percent capacity, and there were few signs the surge was nearing an end.

In October, Mass General Brigham saw 2,000 cases of the virus. It has seen another 1,000 cases in just the first week of November. Of those, 250 have required some level of hospitalization, and 10 to 20 percent have required intensive care unit beds.

Each year, RSV lands 58,000 to 80,000 children younger than 5 in the hospital, according to the Centers for Disease Control and Prevention. But this year, the virus has struck earlier than usual, likely because masking and social distancing during the first two years of the pandemic prevented children from developing immunity to RSV and other common bugs. Mass General Brigham clinicians also said this year’s surge is higher than what is typically seen in the winter months.

Clinicians noted that the vast majority of children infected with RSV recover.

“Usually those hospitalizations are brief, but it can be very severe,” said Dr. Brian Cummings, medical director in the Department of Pediatrics at Mass General for Children. “And so some patients may need breathing support in the pediatric intensive care unit.”

Boston Children’s Hospital said it has been at or over capacity for nearly six weeks and expected its number of patients would continue to climb into the winter. The hospital was postponing surgical cases where a delay wouldn’t be detrimental to a patient.

“We reach out to patients and families as soon as we know their case is being postponed,” said Kristen Dattoli, a spokesperson for the hospital. “We recognize this is upsetting to everyone.”

Boston Medical Center said it, too, had postponed several scheduled surgeries and was working daily with hospitals in the area to manage inpatient capacity.

Baystate Children’s Hospital is also delaying what few scheduled surgeries it has. It is also trying to create capacity in other ways. The pediatric hospital has asked community hospitals affiliated with the system to keep 18-to-21-year-old patients instead of sending them to the children’s hospital as they normally would. Overflow pediatric beds are also being put in the adult medical intensive care unit.

Meanwhile, the hospital is warily eyeing the rise in flu infections in Connecticut and the southern part of the country.

“We don’t have the beds for kids now for RSV and other respiratory viruses,” said Dr. Charlotte Boney, pediatrician-in-chief at Baystate Children’s Hospital. “We’re really worried about flu.”

Last Monday, the Department of Public Health issued guidance to hospitals dealing with the capacity crunch. The guidance included a recommendation that all emergency departments be prepared to provide oxygen support to children through high-flow nasal cannula — a treatment that patients would typically receive on a hospital floor after being admitted.

“Hopefully that frees up [beds],” Boney said.

The guidance added that all hospitals with licensed pediatric beds must be staffing them, even if it requires the facility to use temporary or contract labor to do so.

The DPH also suggested that younger patients could be admitted to neonatal intensive care units and that patients 15 and older could be admitted to adult medical-surgical or ICU floors, provided that pediatric experts were available to consult on the children’s care.

Hospitals should also use beds available at community hospitals and transfer patients there as appropriate, the guidance says.

Transferring patients to more intensive beds, however, has become exceedingly tricky. According to a rundown of bed availability provided daily by Boston MedFlight to area hospitals and obtained by the Globe, Massachusetts General Hospital’s pediatric intensive care unit was full on Thursday, as were all of its 21 neonatal intensive care unit beds. Brigham and Women’s Hospital had three of 60 NICU beds available.

No beds were available at Boston Medical Center’s or Baystate Medical Center’s pediatric intensive care units, or PICUs. PICUs were also full at New Hampshire’s Dartmouth Hitchcock Medical Center, and Rhode Island’s Hasbro Children’s Hospital. Maine Medical Center had three available PICU beds.

According to Boston MedFlight, as of Thursday morning, there were only four available PICU beds in all of Massachusetts, New Hampshire, Southern Maine, and Rhode Island.

In addition to delaying pediatric surgeries, some hospitals are having to provide care that normally would be delivered in the ICU in lower intensity beds, such as for a child in respiratory distress. And while the use of certain therapies might automatically send a patient to the ICU in the past, now it is a question of whether there is a bed.

“If they need the ICU and a bed is available, we will transfer them there. But we want to make sure we can deliver the care they need if a bed is not available,” Biddinger said. “That’s why lots of systems, including ours, are providing more support from our intensive care physicians and nurses to clinicians on the floor or in the ER, and trying to roll out additional support from respiratory therapists, and increased education on these therapies for clinicians in the pediatric setting overall.”

National data is showing earlier and higher RSV-associated hospitalizations this season than in years past. In the last five years, RSV hospitalizations didn’t peak until December and January. But last month, hospitalizations had already reached or exceeded the peaks of several previous years.

Even hospitals that haven’t yet delayed scheduled surgeries remain concerned about their capacity. South Shore Health said it is not postponing pediatric surgeries, though 14 of its 18 pediatric beds were occupied as of Wednesday morning.

UMass Memorial Medical Center said it was experiencing high pediatric patient volume due to RSV, flu, and COVID, combined with the ongoing behavioral health crisis. On Tuesday, the hospital’s pediatric bed capacity was at 115 percent — meaning that children who have been admitted to the hospital are having to wait in the ER until beds open up.

“At this time, pediatric elective surgeries have not been canceled, however, we continue to monitor the situation and review our bed status and each case to determine whether an elective procedure can be safely deferred or whether we have capacity to proceed,” said Dr. Lawrence Rhein, chair of the hospital’s pediatrics department.

Kay Lazar of the Globe staff contributed to this report.

Jessica Bartlett can be reached at jessica.bartlett@globe.com. Follow her on Twitter @ByJessBartlett.