ATHENS, Greece (CNN) -- A Cypriot plane with "no sign of life" in the cockpit as it approached Athens has crashed into a mountain, killing all 121 people on board, Greek officials said. F-16 pilots escorting the jet after air traffic controllers lost contact with it said the pilot was not in the cockpit and the co-pilot was slumped over the controls, according to reports. The pilots of the Helios Airlines Boeing 737 had reported an air conditioning problem, and Greek TV said a passenger sent a text message to his cousin saying it was freezing in the plane. "The pilot has turned blue (in the face)," the passenger said in the SMS message, Reuters quoted the television report as saying. "Cousin farewell we're freezing." The plane, Helios Flight 522 with 115 passengers and six crew en route from Larnaca, Cyprus to Athens, crashed about 12 p.m. Sunday (0900 GMT, 5 a.m. ET), officials said. The Greek government said there were no survivors. The plane was supposed to continue to Prague, Czech Republic after landing in Athens, according to the Czech Press Agency, citing officials at the Prague airport. The passengers included 59 adults and eight children who were disembarking at Athens for a vacation, the government said, along with 46 adults and two children who were headed to Prague. Akrivos Tsolakis, head of the Greek airline safety committee, called the crash the "worst accident we've ever had," The Associated Press reported. Greek officials said they suspect malfunctions in the oxygen supply or pressurization system could have caused the crash. Greek police said there were no signs the plane had been hijacked, Reuters reported. The jet crashed near the coastal town of Grammatikos, about 40 km (25 miles) north of Athens and near the historic town of Marathon. The crash site was littered with bodies and debris, Athens journalist Paul Anastasi told CNN. Video footage from the site showed the smoking wreckage of the aircraft. Only the tail portion remained identifiable. The crash sparked forest fires, which officials said were hindering recovery efforts. "There is wreckage everywhere," Grammatikos Mayor George Papageorgiou told AP from the scene. "The fuselage has been destroyed. It fell into a chasm and there are pieces. All the residents are here trying to help." One witness told Reuters: "I saw many bodies scattered around, all of them wearing (oxygen) masks. The tail was cut off and the remaining parts of the plane rolled down a hillside about 500 metres away from the tail." The jet entered Greek air space about 10:30 a.m., but efforts by air traffic controllers to contact the pilots were futile. After some time, two Greek F-16s were scrambled, Greek Air Force spokesman Yiannis Papageorgiou told CNN. As the F-16s approached, their pilots saw "no sign of life" in the cockpit, and the plane apparently was on autopilot, Papageorgiou said. The F-16 pilots reported the pilot was not in the cockpit, and the co-pilot was slumped over the controls, Anastasi said. They also reported they could see through the plane's windows that the oxygen masks had dropped down. The F-16s escorted the plane until it struck the mountain. "Although there are precedents for both pilots losing consciousness at the controls of aircraft in the past, for it to happen on a large airliner like a Boeing 737, with all the backup systems they have there, does seem to be really quite extraordinary," said Kieran Daly, editor of Air Transport Intelligence. "It really is all very peculiar at the moment, I rather suspect we're heading for a very complicated investigation," he said. A lack of oxygen apparently caused the crash that killed golfer Payne Stewart in the U.S. state of South Dakota in 1999. Stewart's twin-engine jet went down in a pasture after flying halfway across the country on autopilot, as Stewart and the four others aboard apparently lay unconscious for lack of oxygen after the plane lost cabin pressure. Everyone was killed. In Greece, witness Dimitris Karezas, who owns a summer camp in the area of Sunday's crash, told Reuters, "I saw the plane coming. I knew it was serious or that it was some kind of VIP because I saw the two fighter jets. "Two, three minutes later I heard a big bang and ever since I've started looking for it, but I have not found anything yet," he told reporters. A spokeswoman for the Czech Airport Authority, Anna Kovarikova, told Reuters the flight had been due to land in Prague at 1:10 p.m. (1110 GMT). At the Prague airport, where friends and relatives were gathering to meet the flight, screens showing departures and arrivals read simply "delayed" next to the stricken flight. Helios Airlines is a subsidiary of Cyprus Airlines. On Sun, 14 Aug 2005, Ian Caldwell wrote: > From the BBC http://news.bbc.co.uk/1/hi/world/europe/4150312.stm > > A Cypriot airliner carrying 121 people has crashed near Athens after an > apparent drop in cabin pressure led to a dramatic fall in temperature. > > The Boeing 737 plane, carrying 115 passengers and six crew, came down at > 1220 local time (0920 GMT). >