(CNN)"A picture of horror." That's how German Foreign Minister Frank-Walter Steinmeier described the site where a Germanwings Airbus A320 plane crashed in the French Alps on Tuesday. "The grief of the families and loved ones is immeasurable," Steinmeier said, after flying over the area in the Alps in southeastern France. "We must stand with them. We are all united in great grief." Flight 9525 took off just after 10 a.m. Tuesday from Barcelona, Spain, for Dusseldorf, Germany, with 144 passengers -- among them two babies -- and six crew members. It went down at 10:53 a.m. (5:53 a.m. ET) in a remote area near Digne-les-Bains in the Alpes de Haute Provence region. All aboard are presumed dead. Helicopter crews found the airliner in pieces, none of them bigger than a small car, and human remains strewn for several hundred meters, according to Gilbert Sauvan, a high-level official in the Alpes de Haute Provence region who is being briefed on the operation. Authorities were not able to retrieve any bodies Tuesday, with the frozen ground complicating the effort. Wednesday may not be much easier, with snow in the forecast. Spanish and German officials moved to join hundreds of French firefighters and police in the area, working together to help in the recovery effort and try to figure out exactly what happened. As of Tuesday evening, there were few clues. One of the aircraft's data recorders, the so-called black boxes, has been found, according to French Interior Minister Bernard Cazeneuve, but it was too early to tell what it would say about the crash. "We don't know much about the flight and the crash yet," German Chancellor Angela Merkel said. "And we don't know the cause."Students, teachers among the victims Relatives of those believed to be on the flight, fearing the worst, gathered at the Barcelona airport, where a crisis center was set up. French authorities set up a chapel near the crash site. Lufthansa Group said the company will look after the relatives of those on board. "There will be a contact center established in France; relatives who would like to take advantage of this will be transferred to the contact center at no cost -- and their accommodation paid for -- just as soon as the center has been established," Lufthansa said. Those aboard included a "high number of Spaniards, Germans and Turks," according to Spain's King Felipe VI. Germanwings CEO Thomas Winkelmann said it's believed 67 people, or nearly half those on the plane, are German citizens. Sixteen students and two teachers from one German high school, called Joseph Koenig Gymnasium, were among those booked on Flight 9525, according to Florian Adamik, a municipal official in Haltern, the town where the school is located. A crisis center has been established at the city hall in Haltern, which is about 77 kilometers (48 miles) north of Dusseldorf's airport. Winkelmann confirmed the 16 students and two teachers were on the plane. Haltern's mayor, Bodo Klimpel, said they had been heading home after taking part in a foreign exchange program. "The whole city is shocked, and we can feel it everywhere," Klimpel said. A Dutch citizen and a Belgian -- the latter a resident of Barcelona -- were among those on the flight, according to those countries' foreign ministries. Two Australians and two Colombians were also believed to be on board.