SEYNE-LES-ALPES, France — A black box recovered from the scene and pulverized pieces of debris strewn across Alpine mountainsides held clues to what caused a German jetliner to take an unexplained eight-minute dive Tuesday midway through a flight from Spain to Germany, apparently killing all 150 people on board.

The victims included two babies, two opera singers and 16 German high school students and their teachers returning from an exchange trip to Spain. It was the deadliest crash in France in decades.

The Airbus A320 operated by Germanwings, a budget subsidiary of Lufthansa, was less than an hour from landing in Duesseldorf on a flight from Barcelona when it unexpectedly went into a rapid descent. The pilots sent out no distress call and had lost radio contact with their control centre, France’s aviation authority said, deepening the mystery.

While investigators searched through debris from Flight 9525 on steep and desolate slopes, families across Europe reeled with shock and grief. Sobbing relatives at both airports were led away by airport workers and crisis counsellors.

“The site is a picture of horror. The grief of the families and friends is immeasurable,” German Foreign Minister Frank-Walter Steinmeier said after being flown over the crash scene. “We must now stand together. We are united in our great grief.”

It took investigators hours to reach the site, led by mountain guides to the craggy ravine in the southern French Alps, not far from the Italian border and the French Riviera.

Video shot from a helicopter and aired by BFM TV showed rescuers walking in the crevices of a rocky mountainside scattered with plane parts. Photos of the crash site showed white flecks of debris across a mountain and larger airplane body sections with windows. A helicopter crew that landed briefly in the area saw no signs of life, French officials said.

“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 general council, Alpes-de-Haute-Provence, told The Associated Press.

“This is pretty much the worst thing you can imagine,” said Bodo Klimpel, mayor of the German town of Haltern, rent with sorrow after losing 16 tenth graders and their two teachers.

The White House and the airline chief said there was no sign that terrorism was involved, and German Chancellor Angela Merkel urged reporters not to speculate on the cause.

“We still don’t know much beyond the bare information on the flight, and there should be no speculation on the cause of the crash,” she said in Berlin. “All that will be investigated thoroughly.”

Lufthansa Vice-President Heike Birlenbach told reporters in Barcelona that for now “we say it is an accident.”

Friends of the German students from the crashed plane attend a mass in Llinars del Valles, near Barcelona, Spain, Tuesday, March 24, 2015. Sixteen 10th-grade students from a town in western Germany and two of their teachers had just spent a week on an exchange near Barcelona and were less than an hour from landing when their Germanwings flight crashed in southern France.