Six people were killed when two helicopters collided in Rio de Janeiro, Brazil, on Sunday morning. The crash occurred in the western suburb of Recreio dos Bandeirantes, where both aircraft went down in the parking lot of an electric car dealership. Authorities have launched an investigation to determine the cause of the collision.

According to the Brazilian fire department, the crash ignited a fire that engulfed around 20 vehicles. Fire department spokesperson Fabio Contreras said the lithium-ion batteries in the electric cars released toxic gases, making the fire difficult to control. He explained that such batteries emit highly toxic gases and increase both the heat and intensity of flames.

Contreras added that the area is densely populated, and the death toll could have been much higher if the helicopters had not crashed in the parking lot. Rescuers recovered wreckage from one helicopter containing five bodies, while the other helicopter, found about 328 feet away, contained the pilot’s body.