Investigators on Tuesday recovered the bodies of 10 people, including three celebrated French athletes, who were killed when two helicopters collided during filming of a reality TV program in a remote part of Argentina.
The crash, which occurred Monday in the northwestern province of La Rioja, near the Andes mountains, raised new questions about the safety of adventure-style programs, which have suffered a number of fatal accidents in recent years.
The cause of the crash was not immediately known, but provincial officials said weather was not believed to be a factor.
"An explosion occurred, and it's believed that they must have collided," La Rioja's secretary of security, Cesar Angulo, told reporters.
Amateur footage shared by Argentine media showed what appeared to be the helicopters flying together at low altitude; then one veers into the path of the other and both plummet to the ground.
All 10 people aboard were killed, authorities said.
The bodies were removed from the charred wreckage near Villa Castelli, about 700 miles northwest of the capital, Buenos Aires. Killed were two Olympic medalists, swimmer Camille Muffat and boxer Alexis Vastine, a world-class sailor, Florence Arthaud, the two Argentine pilots and five French members of the production crew.
It was the second time in two years that a program produced by Adventure Line Productions for the popular French television network TF1 has suffered fatalities. In 2013, a 25-year-old contestant died of a heart attack during filming for the long-running endurance show "Koh-Lanta" in Cambodia. The doctor on set later committed suicide.
Nonce Paolini, the chairman and chief executive of TF1, said he did not know the exact circumstances of Monday's crash.
"We are in shock and really very, very, very, very sad," he told the French radio network RTL. "We do this to bring pleasure to people, and there was on the part of the champions great enthusiasm for this adventure game."
France's Air Transport Gendarmerie opened an inquiry into the crash, and two French aviation experts were dispatched to the scene to join the Argentine probe. They will be accompanied by experts from Airbus, whose helicopter subsidiary built the aircraft, and Turbomeca, a French helicopter engine manufacturer.
Local news reports said a mostly French crew numbering about 80 people had been working in the area for several days, doing pre-production work for the show, which flies contestants blindfolded to a remote location and has them find their way back to civilization.
France was plunged into mourning for three sports champions, who in the words of President Francois Hollande "shone for France."
"They are dead because they wanted to push boundaries, explore new countries and lead the way for others," Hollande told reporters at the Elysee Palace in Paris.
French Prime Minister Manuel Valls tweeted his "immense pain after this tragedy." "All of France is grieving this morning," he said.
Thomas Bach, president of the International Olympic Committee, said the world of sport and the Olympic family had lost three key members. "They were all not only champions in their sport but also contributed greatly as role models," he said.
Muffat, 25, won a gold medal and set an Olympic record in the 400-meter freestyle at the 2012 London Games. She also won a silver medal in the 200-meter freestyle and was part of France's bronze-winning 800-meter freestyle relay.
"She had dedicated a lot of her life to swimming ... and her objective since her retirement was to make a success of her [personal] life," her friend and agent Sophie Kamoun told the Associated Press. "She had a lot of projects that made her happy, and this show was one of them."
Muffat's boyfriend, William Forgues, said she had left home happy and loved doing the program.
"People often called Camille 'Madame 100%' because she won everything -- almost everything," he said in a tearful television interview.
Vastine, 28, won a bronze medal in the light-welterweight division at the 2008 Beijing Olympics. His 21-year-old sister died in a car accident in January, and Vastine reportedly decided to appear on "Dropped" to help him deal with the loss.
The pair's father, Alain, said he learned about the fatal helicopter crash on the news.
"How will we recover? I do not know," he was quoted as saying by the French newspaper Le Parisien. "I feel like giving up but I'm not allowed. I'm a boxing teacher. I must continue for the children."
Arthaud, 57, was the first woman to win the Route du Rhum, a solo yacht race across the Atlantic Ocean, in 1990. In 1997, she won the transpacific race, which starts in San Pedro and ends in Honolulu, a distance of about 2,560 miles.
"It's a very sad end for a woman who was all about joy, all about life," friend and fellow sailor Philippe Poupon told RTL.
The two pilots, both graduates of Argentine military schools with long experience flying helicopters, were identified by local authorities as Roberto Abate and Juan Carlos Castillo.
The helicopters were provided by the provinces of La Rioja and Santiago del Estero. Both aircraft were in good condition, according to La Rioja Gov. Luis Beder Herrera, who said the model was the "best in the world" for high mountain flying.
The other victims were identified in French news reports as Laurent Sbasnik, Lucie Mei-Dalby, Volodia Guinard, Brice Guilbert and Edouard Gilles. Filming was suspended and the remaining contestants and crew were heading home, the reports said.
Among them was Sylvain Wiltord, a two-time Premier League and FA Cup champion with Arsenal, who tweeted: "I'm sad for my friends, I'm trembling, I'm horrified, I have no words, I don't want to say anything."
Special correspondents D'Alessandro reported from Buenos Aires and Boyle from London. Staff writer Zavis reported from Los Angeles. Staff writer Houston Mitchell contributed from Los Angeles and special correspondent Chris Kraul from Bogota, Colombia.