THE crash of an Airbus passenger plane in the French Alps has killed all 150 people on board.

French prime minister Manuel Valls said a helicopter had managed to land near the crash site and had found no survivors.

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There were reports that the plane had disintegrated, with the largest debris the size of a car.

It is thought that those who died included 16 German schoolchildren, two teachers and two babies.

The Airbus A320, with 144 passengers and six crew on board was being operated by German low-fare airline Germanwings on a flight from Barcelona to Dusseldorf.

Germanwings chief executive Thomas Winkelmann said the aircraft began descending again shortly after it reached its cruising height, having taken off from Barcelona at about 10am local time.

This descent lasted eight minutes, he told reporters in Cologne. Radar and air traffic control contact broke off at 10.53am.

Germanwings said it was thought that 63 of the passengers on board were Germans, while reports from Spain suggest that around 45 Spaniards may have been on the flight.

It was reported that the schoolchildren and teachers had been taking part in a school exchange programme.

Mr Winkelmann said there was still some confusion as to whether a distress signal had been sent from the plane, which came down in a remote area near a popular ski resort.

He said the captain on board was experienced and had been with the airline and with Germanwings' parent company Lufthansa for more than 10 years and had clocked up 6,000 flying hours on this particular Airbus model.

Mr Winkelmann said the plane had had a normal service at Dusseldorf yesterday and its last major check-up had been in the summer of 2013.

He added that teams from Germanwings were in Dusseldorf with the families of those on board and that Lufthansa and Germanwings' technical staff were on their way to the crash site to assist with the investigation.

Prime Minister David Cameron and Deputy Prime Minister Nick Clegg said their thoughts were with the families of the passengers.

Mr Valls said a helicopter had managed to land near the crash site. Gilbert Sauvan, an official with the local council, told Les Echos newspaper: "The plane is disintegrated. The largest debris is the size of a car."

German chancellor Angela Merkel, Spanish prime minister Mariano Rajoy and French president Francois Hollande have all expressed their sorrow.

Mr Cameron's official spokesman said the Prime Minister had been informed of the crash and "would wish to express how his thoughts are very much with the families and friends of all of those aboard".

He added that the Foreign Office was making inquiries about whether any British nationals were on board, but had no information at this stage.

He said UK air accident investigators would offer any assistance requested by French or German authorities.

Mr Clegg said: "My heart goes out to the family and friends of those people who appear to have lost their lives in this devastating air crash in the Alps."

French ministers were on their way to the crash site.

Among them was environment minister Segolene Royal, who was in London for a meeting with the Prince of Wales, which she cancelled to head back to France.

Spain's King Philip VI and Queen Letizia officially cancelled their state visit to France after they were told about the crash by Mr Valls.

It is thought the Germans on board were tourists who had been visiting Barcelona and Palma in Majorca. There were also reports that some Turks were on the flight.

UK weather experts said conditions in the area at the time of the crash were "nothing out of the ordinary".

The weather in the area deteriorated on Tuesday afternoon, with a chilly rain falling.