Investigators on Wednesday scoured the pulverised debris of a German airliner for bodies and clues to the Airbus' mysterious eight-minute descent and crash in the French Alps, killing all 150 people aboard.
Hundreds of firefighters and police near the hamlet of Le Vernet launched a massive operation at the rugged crash site, accessible only by helicopter or by an arduous hike in on foot.
Meanwhile in Paris experts were to analyse one of the plane's black boxes for clues as to why the Germanwings Airbus A320 went down in good weather.
Lufthansa chief Carsten Spohr said the plane of its Germanwings subsidiary that crashed in the Alps was "in perfect condition".
"It is inexplicable," he said when asked if he had further information on the cause of the crash.
"The plane was in perfect condition and the two pilots were experienced."
French President Francois Hollande and his counterparts from Germany and Spain were due to visit the crash site at 2:00pm (1300 GMT) to pay their respects to the mainly German and Spanish victims of the disaster -- the worst on French soil in four decades.
The examination of the damaged black box, which records conversations and noises in the cockpit, would begin "in the coming hours," pledged French interior minister Bernard Cazeneuve.
Transport minister Alain Vidalies said that if voices have been recorded, the investigation would proceed "fairly quickly."
"After that, if we have to analyse the sounds, that's a job that will take several weeks, but it's a job that can offer us some explanations," Vidalies told French radio.
A second black box, in this case recording flight data, has yet to be found.
Officials are hunting for clues to why the plane, operated by Germanwings, Lufthansa's budget subsidiary, entered a fatal eight-minute descent on its route between Barcelona and Duesseldorf.
No distress signal was sent and the crew failed to respond to desperate attempts at contact from ground control.
French police set up road blocks near the crash site, ordering all non-official vehicles to turn around, said an AFP reporter on the scene.
Just beyond lay a steep and broken landscape littered with the shattered pieces of what was flight 4U9525.
"It's a zone that is very difficult to access, very slippery. There was rain and snow overnight. So we need to secure the zone before the investigators begin their work," a spokesperson for the French interior ministry, Pierre-Henry Brandet, told reporters.
"We are not in a race against time," he said. "We need to move forward methodically."
The plane was "totally destroyed", a local member of parliament who flew over the site said, describing the scene as "horrendous".
"The biggest body parts we identified are no bigger than a briefcase," one investigator said.
More than 300 policemen and 380 firefighters have been mobilised for the grisly task of searching the site.
"Ground access is horrible.... It's a very high mountainous area, very steep and it's terrible to get there except from the air during winter," local resident Francoise Pie said.
Meanwhile, family members of the dead were to arrive Wednesday at a village near the crash site, where a counselling centre had been established.
The plane was carrying six crew and 144 passengers, including 16 German teenagers returning home from a school trip.
Their high school in the small German town of Haltern was to hold a memorial event Wednesday to honour the victims.
"This is certainly the darkest day in the history of our city," said a tearful Bodo Klimpel, the town's mayor. "It is the worst thing you can imagine."
Spain, meanwhile, declared three days of mourning and was to hold a minute of silence across the country at noon Wednesday.
Spanish King Felipe VI cut short his first state visit to France on Tuesday minutes after it began when he heard news of the tragedy.
Opera singers Oleg Bryjak, 54, and Maria Radner, 33, were also on board, flying to their home city of Duesseldorf. Radner was travelling with her husband and baby, one of two infants on board the plane.
Assumed to be 'accident'
As the probe gathered pace, Cazeneuve said investigators were not focusing on the possibility it was a terrorist attack.
Germanwings, the growing low-cost subsidiary of the prestigious Lufthansa carrier, had an unblemished safety record and there was still no clue as to what could have caused the disaster.
Weather did not appear to be a factor in the crash, with conditions calm at the time, French weather officials said.
Lufthansa said it was working on the assumption that the crash was an "accident".
"Anything else would be speculation," Lufthansa vice-president Heike Birlenbach told reporters in Barcelona.
She said the 24-year-old Airbus A320 had undergone its last routine safety check on Monday.
Germanwings executive Thomas Winkelmann said the pilot at the controls had "more than 10 years of experience" and some 6,000 flying hours on an Airbus.
It was the deadliest air crash on the French mainland since 1974 when a Turkish Airlines plane crashed, killing 346 people.
Victims were also feared from Colombia, Argentina, Australia, Japan, Belgium, Denmark, Mexico and Britain, according to officials from these countries.
A Swedish third division football team joined the plane after changing flights at the last minute. "May they rest in peace," Dalkurd FF goalkeeper Frank Pettersson wrote on Twitter.
Crash from the past
Tuesday's air disaster was not the first crash seen at the tiny ski resort of Barcelonette in the French Alps: half a century ago, an Air France plane to Vietnam crashed in the same spot.
The crash took place on September 1, 1953, around 16 kilometres (10 miles) from Barcelonnette, killing 42 people on board.
It came down not far from the wreckage of the Germanwings Airbus A320 that crashed on Tuesday.
The Air France plane was on a night-time flight from Paris to Saigon when it clipped a mountain and crashed into a rocky crevice just before midnight.
The pilot was in touch with air traffic control in Aix-en-Provence just five minutes before the accident to request a rise in altitude to 13,500 feet, and did not raise any alarm.
It was a postman from a nearby village who raised the alert after seeing the plane crash into Mount Cemet just before midnight and burst into flames.
Among the victims was a celebrated French violinist, Jacques Thibaud.
Video:Rescuers search for clues