All 121 people on board a Cypriot airliner are feared dead after it plunged into a hill near Athens after an apparent drop in cabin pressure.
A text message sent from the plane said that the pilots were unconscious and passengers were freezing to death.
Greek F-16 fighter jets were scrambled when contact with the Helios Airways plane was lost during the flight between Larnaca in Cyprus and Athens.
Greek television said the plane's black box recorders had been recovered.
Relatives of some of the passengers gathered anxiously at Larnaca airport, and complained they had waited for hours without being told of their loved ones' fates.
"Tell us if our relatives are dead," some begged Helios officials. "Give us the names, we have waited too long."
But there was no confirmation of the identity or nationality of those on board.
"My son is a pilot and he flew to Athens today. I don't know what plane he was on," a distraught mother said.
However, a Greek police spokeswoman said there were no reports of survivors.
The Boeing 737 plane, carrying 115 passengers and six crew, came down at 1220 local time (0920 GMT).
Airline officials said the plane was due to fly on to the Czech capital Prague after a stopover in Athens.
A Greek police spokesman quoted by Reuters said of the passengers, 59 adults and eight children were heading to Athens, with 48 continuing on to Prague.
Larnaca airport authorities told Cyprus state TV a sudden drop in cabin pressure may have knocked out the pilots.
Greek TV reported that a passenger sent a text message to a cousin telling him that the pilot had turned blue in the face and the plane's temperature had plummeted.
"My cousin I bid you farewell, we are all frozen," the text message read.
There were initially suspicions the plane might have been hijacked, but these were swiftly ruled out by Greece's foreign ministry.
A Greek government spokesman said the first indication was that the crash was an accident.
The head of air traffic control at Athens airport, Iannis Pantazaratos, told AFP that authorities lost contact with the plane, and air force pilots found it flying above the Euboea peninsula with the pilots slumped in the cabin.
Both Greek Prime Minister Costas Karamanlis and his Cypriot counterpart Tassos Papadopolous cut short holidays to return to Athens and Larnaca respectively.
Police and military helicopters were sent to the scene, along with dozens of ambulances.
1999: Established as first independent airline in Cyprus
2000: First chartered flight
2001: First scheduled flight
Flies to UK, Strasbourg, Sofia, Athens, Dublin, Warsaw and Prague
Operates four Boeing 737 planes
TV pictures showed wreckage over a wide area, with firefighters dousing flames on the bare hillside.
The mayor of Grammatikos, one of the towns near the crash site, said only the tail was recognisable.
"The fuselage has been destroyed. It fell into a chasm and there are pieces. All the residents are here trying to help," George Papageorgiou said.
One eyewitness, Dimitris Karezas, told the Reuters news agency he saw the plane being followed by 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 said.
Another said: "I saw many bodies scattered around, all of them wearing [oxygen] masks."
Helios Airways was founded in 1999 as Cyprus' first independent airline.
It operates a fleet of Boeing 737 jets between Cyprus and London, Athens, Sofia, Dublin and Strasbourg in France.
The crash is the worst airline disaster in Greek history, Reuters reports.
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