Candles burn near a giant photo as people pay tribute to late French Olympic swimmer Camille Muffat in Nice, March 10, 2015. [Photo/Agencies]

BUENOS AIRES/PARIS - France mourned on Tuesday the deaths of three sports stars who were among 10 people killed when two helicopters collided in a remote region of Argentina during the filming of a reality TV show.

Investigators removed the bodies of Olympic swimmer Camille Muffat, yachtswoman Florence Arthaud and boxer Alexis Vastine from the charred wreckage of the two aircraft, but said it was still unclear what caused the accident on Monday afternoon in the rugged western province of La Rioja. There were no survivors.

Amateur footage taken from the ground showed the two helicopters flying in tandem at low altitude when one appears to deviate into the path of the other. Both helicopters then plunge to the ground.

A second video showed dozens of people rushing through the heavy undergrowth toward the helicopters' burning wreckage. The accident occurred around 5.15 p.m. local time (2015 GMT).

French President Francois Hollande paid tribute to the athletes he said had "made France shine".

"They are dead because they wanted to push the boundaries. They wanted to make new exploits known to the world, make people aware of new countries and regions," Hollande said.

In Paris, an involuntary manslaughter investigation has been opened, an automatic procedure when French citizens are killed abroad, a judicial source said.

As part of the TV show, other contestants were standing blindfolded on the ground a few hundred meters from the helicopters' flight path, French media reported. They ran to the crash site but could not extinguish the fire, an assistant to the contestants told French broadcaster RFI.