Authorities said there were 150 people on board flight 4U9525, including 144 passengers and six crew members when it crashed. The passengers included Spaniards,Turks, two Australians, and at least 67 Germans, among them 16 high school students and two teachers who were returning from a study program near Barcelona. The two Australians were Melbourne mother and son Carol and Greig Friday, Foreign Minister Julie Bishop confirmed.

Opera stars bass-baritone Oleg Bryjak, 54, and contralto Maria Radner, 33, were also on board, flying to their home city of Duesseldorf after starring in Richard Wagner's Siegfried at Barcelona's opera house, the Gran Teatre del Liceu. Radner was travelling with her husband and baby, according to the BBC.

The crash site

The plane crashed near the town of Barcelonnette about 100 kilometres north of the French Riviera city of Nice in the south of France.

According to FlightRadar24, a live air traffic website, the site was off course to the original flight. Aerial footage of the crash site showed fragments of debris scattered over a large area on the sides of mountains.

The flight

The aircraft landed in Barcelona at 7:57 GMT and, with a scheduled take-off time of 8:35. It had been grounded in Dusseldorf earlier in the day for an hour because of a problem with the nose wheel door – which Germanwings said had been resolved – then took off more than 25 minutes late from Barcelona for reasons which are not yet clear.

By 9:01 the Airbus was back in the air. All was normal for the next 40 minutes. The Airbus reached a cruising altitude of 38,000ft at 9.45 in the skies over southern France. Then something went catastrophically wrong and the aircraft went into a steep and terminal descent. For the next eight minutes, the aircraft plunged to earth at a rate of 4000 feet per minute. No mayday signal was sent during the fall. It remained intact, automatically relaying its altitude, airspeed and heading. At 9:47, air traffic controllers implemented an aircraft distress alert, based on its rapid loss of height. At 9:53, all contact was lost.

The reasons

It is not yet known what caused the plane into a steady and rapid descent from 38,000 feet until it hit a mountainside in the Alps halfway through its 90-minute journey from Barcelona to Dusseldorf. It is known the plane's descent took eight minutes, which is longer than the average three or four minutes that would normally be expected in the case of a sudden midair upset such as an aerodynamic stall.

Ms Bishop said it would be premature to speculate about the cause of the crash, but noted that Lufthansa was working on the assumption it was an accident.

The recovery effort

After night fell in southern France on Tuesday, emergency services stopped helicopter flights to the crash site due to safety concerns but police said search teams would stay overnight at altitude. Rescue and crash investigation work would begin again at first light - around 4:30pm Wednesday ADST.

Australian consular officials would set up a mobile office in the French town of Gap, near the crash site, to help with the identification and recovery of the bodies.

Airtravel safety

The Airbus A320 is one of the world's most widely used aircraft, with a plane in the A320 family either taking off or landing every 2.5 seconds, Airbus data shows. But the short-haul, single-aisle A320 has also been at the centre of a dozen fatal accidents since 1988, including in December, when an AirAsia jet crashed into the Java Sea, killing 162 passengers and crew.

With the crash investigation just beginning, airline experts said the A320 was nonetheless an incredibly safe jet showing few causes for widespread alarm. For every million takeoffs, the A320 family has 0.14 fatal accidents, a Boeing safety analysis found.

Fairfax Media with agencies, BBC, Daily Telegraph London