An Airbus A320, without warning or distress signal, abruptly left its cruise altitude as it approached the French Alps Tuesday and began a steep but controlled descent lasting eight minutes before slamming into a remote, snowy mountainside, killing all 150 people on board.

Rescuers struggled for hours to reach the rugged crash site but no one on board Germanwings Flight 9525 from Barcelona to Dusseldorf had survived the horrific crash.

No distress call was made to air-traffic controllers, French officials said, suggesting some sort of relatively sudden event – perhaps a depressurization and failure to don oxygen masks – that left both pilots incapacitated. The controlled dive, albeit steeper than normal, suggested the aircraft was on autopilot.

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"A helicopter managed to land [by the crash site] and has confirmed that unfortunately there were no survivors," French Prime Minister Manuel Valls told parliament, the National Assembly.

Investigators said one of two so-called black boxes – either the flight data recorder or the cockpit voice recorder – had already been recovered from the crash site where the Airbus disintegrated, about 100 kilometres north of the French coastal city of Nice.

Searchers and rescue teams, carried by French military helicopters, located the crash site but difficult and dangerous terrain prevented large-scale recovery operations on Tuesday.

"Everything is pulverized. The largest pieces of debris are the size of a small car. No one can access the site from the ground," Gilbert Sauvan, president of the Alpes-de-Haute-Provence regional council, told the Associated Press.

"It's unlikely any bodies will be airlifted until Wednesday," regional police chief David Galtier said.

Air-traffic controllers monitoring the area saw the Germanwings flight suddenly deviate from its assigned flight altitude of 11,600 metres. Controllers attempted, unsuccessfully, to contact the pilots.

Radar tracked the descending A320. The aircraft's transponder – a device that broadcasts the flight identifier, speed, direction and altitude – continued to broadcast as the aircraft rapidly descended.

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"The aircraft's contact with French radar, French air-traffic controllers, ended at 10:53 a.m.," Germanwings' managing director Thomas Winkelmann told a news conference. He also confirmed that a routine maintenance check had been performed on Monday by technicians from Lufthansa, the parent company of Germanwings.

"The aircraft did not itself make a distress call but it was the combination of the loss of radio contact and the aircraft's descent which led the controller to implement the distress phase," said a spokesman from France's Directorate General for Civil Aviation.

France's aviation investigation bureau, BEA, will lead the probe into the worst crash in France since a Concorde crashed just after takeoff from Paris in 2000.

The length of time – eight minutes – during which Flight 9525 maintained a steady northerly course while descending more steeply than usual and headed directly toward the Alps, coupled with the lack of communication from either the cockpit or passengers with their cellphones, is indicative of an incapacitation event.

Other aircraft have flown, either until fuel exhaustion or into mountains, after pilot incapacitation, usually linked to hypoxia or lack of oxygen after a depressurization at high altitude.

Oxygen for both passengers and larger separate reservoirs for pilots is carried on all modern commercial airliners but unless masks are donned quickly and the supply flows properly, hypoxia can incapacitate within seconds.

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In 2005, a Helios Boeing 737 crashed into a mountain near Athens after a flight from Cyprus, killing all 121 passengers and crew, after a lack of oxygen incapacitated the pilots. That aircraft flew for nearly three hours on autopilot after a pressurization failure left everyone on board unconscious, before it ran out of fuel and crashed.

Nothing suggested a hijacking or a bomb on board the Germanwings flight.

Both pilots, four flight attendants and all 144 passengers on board were killed.

Among them were a group of 16 teenage students and two teachers returning from a school trip to Barcelona.

At least 67 Germans were on board. In Madrid, officials said 45 Spanish citizens were also on Flight 9525. At least one Dutch national and a Belgian were also reported on board.

The Airbus A320 that crashed was 24 years old and owned by Lufthansa since it was manufactured in 1991, according to Airbus. It had made 46,700 flights totalling 58,300 flying hours, which is typical usage for an aircraft of that age.

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More than 6,200 of the twin-engined, medium-range airliner, which comes in several variants, are flying with scores of airlines all around the world. The Airbus A320 variants along with the similar-sized family of Boeing's 737 variants are the workhorses of the world's short- and medium-range routes.

Lufthansa hasn't suffered a major crash for decades. Its worst crash was in 1974 when a Boeing 747 crashed just after take off from Nairobi, but 98 of the 157 on board survived.

In 1979, a Lufthansa cargo Boeing 707 flight from Rio de Janeiro to Dakar crashed into a mountain shortly after takeoff, killing all three crew members on board.

The airline's most recent fatal crash involved another Airbus A320 in 1993 that ran off the end of the runway into an embankment after landing at Warsaw, killing the co-pilot and one passenger.

With a report from Associated Press

With a report from Associated Press