RESCUE workers and investigators were last night combing the wreckage of ill-fated flight ZU 522 after an airline that carries thousands of Britons on budget trips to Cyprus suffered a mystery crash.

Initial reports stated that the pilot was missing from the flightdeck and the co-pilot was seen slumped unconscious in his seat.

All 121 people on board the Helios Airways flight, including 48 children, were killed when the Boeing 737 crashed into a mountain north of Athens.

The only piece of the plane that remained intact was the tail.

The cause of the disaster was unclear, but first indications were that it was due to a technical problem - possibly decompression.

After the Athens control tower lost touch with the aircraft, the Greek air force scrambled two F-16 fighter jets - standard procedure after an aircraft entering the country's airspace does not respond to radio calls.

Greece's Alpha television channel reported that the fighter pilots who intercepted the plane saw one of the pilots slumped unconscious over the controls.

Sotiris Voutas, a cousin of one of the passengers on the plane, told Alpha that he received a text message from the cousin minutes before the crash.

He said: "He told me the pilots were unconscious. He said 'Farewell, cousin, here we're frozen'."

The families were being given confirmation of the deaths of their loved ones last night at Larnaca airport.

The British Foreign Office said it was unable to confirm any passenger details, and the airline spokesman could not say whether any Britons had been on the flight. A colleague said most of the passengers were Greek Cypriots.

The spokesman said: "Unfortunately, our flight 522 from Larnaca to Athens and Prague, carrying 115 passengers and six crew members, crashed north of Athens at approximately 12.20pm (10.20am BST).

"Fire and rescue services are presently at the scene, and it isn't clear as to why the aircraft crashed.

"Our thoughts are with the families of those on board at this very difficult time, and we are doing absolutely everything we can within our power to keep people informed about this accident."

Greek state television quoted Cyprus Transport Minister Haris Thrasou as saying the plane had had problems with decompression in the past.

UK and Cyprus-registered tour operator Libra Holidays Group bought Helios last year.

The low-cost carrier was established as the first independent privately-owned airline in Cyprus, in 1999, and operated its first chartered flight to Gatwick in May 2000.

Its fleet of Boeing B737s operates scheduled flights from Larnaca and Paphos to a range of airports, the majority of which are in the UK, and include Newcastle, Luton, Heathrow, Gatwick, Stansted, Manchester, Birmingham, Glasgow, Nottingham, Belfast and Dublin.

Charter service bases operate from Teesside, Newcastle and Humberside, as well as other European cities.

A Newcastle Airport spokesman said last night: "Helios has a weekly scheduled flight from Newcastle to Larnaca, in Cyprus. Until we hear otherwise we do not know whether this will be affected.

"There will be people who have booked to go out on Saturday and people who are looking to return.

"People should look at our website or contact their tour operators to find out more information. The company only has four aircraft, so we hope they have got some contingency plan in place."

An emergency number - 00 357 22 446146 - has been issued for families worried their relatives were on board.