A flight attendant has died after the cabin of the plane he was working on filled with smoke

• A flight attendant working for Swiss Air has died after a plane's cabin filled with smoke mid-flight.
• On December 23, a flight from Bucharest to Zurich diverted due to engine issues and smoke.
• The staff member, who hasn't been named, died around a week after being taken to hospital.

A young Swiss International Air Lines flight attendant died after smoke started to fill the cabin and cockpit.

The flight — operating from Bucharest in Romania to Switzerland's Zurich on December 23 — made an emergency diversion to Graz in southern Austria after engine problems led smoke to spread through the plane, according to a press release by the airline.

The member of staff, who has not been named publicly, was airlifted to a hospital in Graz, where he was put into intensive care. He died on Monday, December 30.

"We are devastated at our dear colleague's death," Swiss CEO Jens Fehlinger said in a statement.

"We stand with one another at this truly difficult time; and we will be doing our utmost, together with the relevant authorities, to determine the causes involved," Oliver Buchhofer, the airline's chief operating officer added.

"We have many questions, and we want them answered," he added.

All 74 passengers on board the Airbus A220 were evacuated, and twelve received medical attention. All five crew members were placed under medical care.

"Our teams of experts are working hard over the festive season to evaluate all the facts and findings available, and are in close contact with the authorities," the airline said in a statement about the investigations into the incident.

The focus of the investigation is on the mechanical parts of the aircraft — like the engine — and the protective breathing equipment available to the cabin crew.

SWISS announced it was working with the relevant authorities, the engine manufacturer Pratt & Whitney, and the aircraft manufacturer Airbus.

"The initial findings point to a technical problem in one of the engines," it said in the press release, but the cause of the smoke has not yet been conclusively determined.

A special flight from Graz to Zurich was organized on the morning of Christmas Eve to get passengers to their destination.