Seyne-les-Alpes (France) (AFP) - Investigators on Wednesday made their first breakthrough in the probe into the crash of an airliner in the French Alps, as President Francois Hollande vowed everything would be done to explain the tragedy that killed 150 people.
Officials from the BEA crash investigation agency said they had extracted "usable data" from one of the Germanwings Airbus A320's two "black boxes" found among the debris, with recordings from the cockpit, but still had no explanation for the mysterious crash.
Hollande and German Chancellor Angela Merkel flew over the crash site to see the devastation for themselves before meeting rescue workers outside the crisis centre set up on Tuesday after the worst crash in France in four decades.
Spain's Prime Minister Mariano Rajoy also visited the centre to be briefed on the gruelling rescue operation in difficult mountain terrain where Flight 4U9525 crashed early Tuesday, scattering debris over a wide area.
Buffeted by strong mountain winds, the ashen-faced leaders spent several minutes inspecting a line-up of blue-uniformed rescue workers, chatting intently with the help of interpreters.
"My deepest sympathies with the families and all my thanks for the friendship of the people of this region and in France," wrote Merkel in a book of condolence.
Grieving relatives were also gathering near the crash site, where a counselling unit has been established.
A further wave of families was expected to arrive Thursday morning aboard two special Lufthansa flights from Spain and Germany.
Lufthansa chief executive Carsten Spohr told reporters the flights would leave for Marseille from Barcelona, departure point of the stricken flight, and Duesseldorf, its destination.
Authorities in France said the family members would be taken as close to the crash site as possible.
"We have to understand what happened. We owe it to the families and the countries concerned by the drama," Hollande told reporters, vowing to shed light on the mystery.
"What has happened is the worst thing that can befall a human being," said Rajoy.
- 'Not the slightest explanation' -
Meanwhile, BEA released photos of the mangled black box, its metal casing torn and twisted by the violence of the impact.
BEA head Remi Jouty told reporters he had "not the slightest explanation" for the crash at this stage, although he revealed the plane was still flying when it smashed into the mountainside and did not explode mid-air.
Hollande said the casing of a second black box, which records technical flight data, had been found but not the device itself.
Authorities are still baffled as to why the plane suddenly began a fatal eight-minute descent shortly after reaching cruising altitude 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.
"It is inexplicable," Lufthansa chief Spohr said in Frankfurt.
"The plane was in perfect condition and the two pilots were experienced."
Officials in Spain said at least 51 Spaniards had been killed in the accident, and Germanwings said at least 72 Germans were dead.
Authorities on the ground who had the gruesome task of sifting through the debris for body parts and clues called off the search later Wednesday and would resume at dawn the following day.
- 'Incredible', 'shocking' scene -
a minute's silence A mountain guide who got near the crash site -- a steep and broken landscape littered with the shattered pieces of Flight 4U9525 -- said he was unable to make out recognisable body parts.
"It's incredible. An Airbus is enormous. When you arrive and there's nothing there ... it's very shocking," said the guide, who did not wish to be identified.
The plane was carrying six crew and 144 passengers, including 16 German teenagers returning home from a school trip.
Bereaved pupils from their high school in the small German town of Haltern wept and hugged near a makeshift memorial of candles as they pulled together to share the pain of losing their friends.
"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."
"Yesterday we were many, today we are alone," read a hand-painted sign at the school, decorated with 16 crosses -- one for each of the victims, most around 15 years old.
Compounding the tragedy, it emerged that those killed had won the trip in a lottery of their classmates, reported local daily the Halterner Zeitung in its online edition.
Also on board were opera singers Oleg Bryjak, 54, and Maria Radner, 33, flying to their home city of Duesseldorf.
Radner was travelling with her husband and baby, one of two infants on board the plane.
In Spain, a minute's silence was observed at noon around the country.
Germanwings, the growing low-cost subsidiary of the prestigious Lufthansa carrier, had an unblemished safety record.
Weather did not appear to be a factor in the crash, with conditions calm at the time.
It was the deadliest air crash on the French mainland since 1974 when a Turkish Airlines plane crashed, killing 346 people.
Victims were also confirmed from Argentina, Australia, Belgium, Britain, Colombia, Denmark, Holland, Israel, Japan, Mexico and the United States, according to officials.