SEYNE-LES-ALPES, France - French, Spanish and German leaders Wednesday visited a makeshift rescue base near the site of the Germanwings air crash, as investigators stepped up their probe into the mysterious disaster that killed 150.
French President Francois 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.
Grieving relatives of the dead were also gathering near the crash site, where a counselling unit has been established.
Meanwhile, investigators were combing through the pulverised wreckage and examining its badly damaged black box for clues as to what caused the mysterious crash.
Hundreds of firefighters and police near the hamlet of Le Vernet in the French Alps were involved in the massive task at the rugged crash site, accessible only by helicopter or an arduous hike on foot.
And in Paris, experts analysed one of the plane's black boxes, hoping to discover why the Airbus A320 went down in good weather - an "inexplicable" disaster according to Lufthansa, the budget airline's parent company.
Photos issued by the BEA air crash investigation office showed a mangled orange "black box", its metal casing torn and twisted by the violence of the impact.
Officials warned it would take several days to analyse the "very badly damaged" black box data, but hoped it might offer initial clues to the mystery later Wednesday.
A second black box, recording technical flight data, has yet to be found.
Authorities are scrambling to explain 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 Carsten Spohr said in Frankfurt.
"The plane was in perfect condition and the two pilots were experienced." Officials in Spain said at least 49 Spaniards had been killed in the accident, and Germanwings said at least 72 Germans were dead.
French police set up road blocks near the crash site, ordering all non-official vehicles to turn around, an AFP reporter at the scene said.
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 spokesman 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 assigned the grisly task of searching the site.
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." "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 of whom were around 15 years old.
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.
In Spain, meanwhile, a minute's silence was observed at noon at countless points around the country, including both houses of parliament in Madrid and public offices.
As the probe gathered pace, Interior Minister Bernard 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.
Weather did not appear to be a factor in the crash, with conditions calm at the time, French weather officials said.
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.