"INEXPLICABLE"

German Chancellor Angela Merkel, French President Francois Hollande and Spanish Prime Minister Mariano Rajoy shake hands with the members of the search team. [Photo/Xinhua]

A tribute ceremony took place on a site with a view in the distance of the mountain against which the Airbus crashed.

Earlier, Lufthansa said it could not explain why the Airbus run by its low-cost Germanwings unit crashed.

"It is inexplicable this could happen to a plane free of technical problems and with an experienced, Lufthansa-trained pilot," its CEO Carsten Spohr told reporters in Frankfurt.

Lufthansa said the 24-year-old plane had just on Monday had repairs to the hatch through which the nose wheel descends for landing. A spokeswoman said that was not a safety issue but that repairs had been done to reduce noise.

Police and forensic teams on foot and in helicopters investigated the site about 100 km (65 miles) north of Nice where the airliner slammed into mountains in what aviation officials was a sharp descent but not freefall.

"When we go to a crash site we expect to find part of the fuselage. But here we see nothing at all," pilot Xavier Roy, coordinating air operations, said of the confetti of debris.

Roy said teams of investigators had been dropped by helicopter onto the site and were working roped together at altitudes of around 2,000 meters (6,000 feet).