A man was nearly sucked head-first out of a cabin window in mid-air on a Ryanair plane, passengers have said.
Tracking data shows the plane was in the air for about 10 minutes when it abruptly descended 9,000ft (2,700m), with passengers telling local media they heard "some kind of explosion".
A Greek hospital official said a 61-year-old Serbian national was being treated for friction burns. "His wife held onto his legs for around five minutes to stop him from being sucked out," Michalis Giannakos said.
In a statement, Ryanair said its Friday morning flight from the Greek city of Thessaloniki to Germany's Memmingen returned "shortly after take-off when a passenger window dislodged in flight".
"The aircraft landed normally and passengers returned to the terminal. One passenger requested and received medical assistance on the ground in Thessaloniki," the Irish budget airline said.
It added that "a replacement aircraft was arranged to bring passengers to Memmingen" several hours later.
Passengers have told local media the man was left hanging head first out of the window as far as his shoulders before other passengers managed to pull him back inside.
Those on board have also said the window was smashed by pieces of the jet's engine - although Ryanair has not commented on this.
"We immediately realised there had been a decompression. There were screams... for a moment I thought someone had accidentally opened the emergency door," Christina, a fellow passenger, told Radio Thessaloniki.
"The masks dropped and there was a strong smell. The head and shoulders of one passenger were outside the window. Fortunately, he hadn't taken off his seat belt."
Another passenger, Sofia, told Radio Thessaloniki: "When the oxygen masks dropped, we had no idea what was going to happen. We didn't know whether we would make it back. We were sitting at the back of the aircraft, and we realised there had been some kind of explosion.
"We thought the plane was going down. The decompression was extreme. It felt like we couldn't breathe. The man who was injured was bleeding and then lost consciousness several times, most likely because of the lack of oxygen and the shock," Sofia added.
Michalis Giannakos, president of the Panhellenic Federation of Public Hospital Employees, later said that a 61-year-old Serbian man was being treated in hospital with friction burns.
"He is in shock, remains conscious" he added.
The aircraft - believed to have been an 18 year-old-plane - was operated by Ryanair's subsidiary Malta Air.
Thessaloniki airport's operator Fraport Greece said "the incident is currently under investigation by the Hellenic Air and Rail Safety Investigation Authority".
Fraport Greece added that it "is fully co-operating with all relevant stakeholders and has activated the established emergency response procedures following the aircraft's forced return".
The Irish Aviation Authority (IAA) earlier told the BBC it was aware of the incident and would provide any assistance to investigators.
Chris Brady, a retired airline pilot, told the BBC the incident "could have been worse" had the seat belt been not fastened.
"We do, as captains always say to the passengers, please keep your seat belts fastened as a precaution in flight, even when we switch the belt signs off.
"And it's for exactly this sort of thing or for turbulence encounters or whatever. So it is good practice to leave your seat belts on," he said.
In 2018, a passenger died when debris from a damaged engine caused a window to break on a Southwest Airlines flight in the US, and she was partially sucked out.
Additional reporting by Mark Allison and Nikos Papanikolaou
