A 46-year-old firefighter died Wednesday after suffering an unspecified medical emergency while on duty at Engine 78 at Philadelphia International Airport, officials said.

Michael Bernstein, a 22-year Fire Department veteran, died after he was taken to Mercy Fitzgerald Hospital in Darby Borough. He was found unconscious in a hallway after he didn’t arrive at his apparatus for dispatch to an airport terminal call, according to the Philadelphia Fire Fighters and Paramedics Union. CPR was started and Bernstein was then taken to the hospital, where he was pronounced dead at 1:50 a.m. Wednesday, the union said.

Further details about the circumstances of his death were not available. “The nature and cause of fatal injury are still to be determined,” the U.S. Fire Administration said.

Mayor Jim Kenney ordered city flags to be flown at half-staff for 30 days in memory of Bernstein, a Navy veteran.

“I’m deeply saddened by the death of Philadelphia Firefighter Michael Bernstein," Kenney said in a statement. “We are humbled by his dedication, and we will always remember his sacrifice. My heartfelt condolences go out to his family, friends, and fellow firefighters.”

Chellie Cameron, the airport’s CEO, also mourned Bernstein’s death.

"Each emergency responder stationed at the airport is a part of our family, and we stand by to support our colleagues during this time of loss,” Cameron said in a statement.

Deputy Chief Robert Corrigan, commander of Fire Department operations at the airport, said in a tweet that Bernstein’s colleagues were “devastated” by his death.

Across the Philadelphia region and elsewhere, the emergency-response community — from the Philadelphia firefighters union to other fire companies to volunteers who work with first responders — paid tribute to Bernstein.

“Rest Easy Brother,” the Second Alarmers, a volunteer group that provides beverages and other sustenance to firefighters and police officers at emergency sites, wrote on Twitter, adding that the group extended its “sincerest condolences to the Philadelphia Fire Department in your loss.”

During his two-decade career, Bernstein was assigned to several engines and ladders across Philadelphia, the Fire Department said. Survivors include his wife and three children, the department said.

Viewings will be held at John F. Givnish Funeral Home, located at 10975 Academy Road, Monday from 5 to 8 p.m. and Tuesday from 9:30 a.m. to 11:30 a.m. Services will take place at St. Jerome Church, located at 8100 Colfax St., at 12:30 p.m. Tuesday. A private burial at Resurrection Cemetery, 5201 Hulmeville Road in Bensalem, will follow.