I've got another movie from my childhood that I'm trying to find.
I saw it on TV (in the US) no later than 1975-76, in English.
The plot was an ongoing end-of-civilization event. There was a small group of people in the woods trying to survive. People would fall asleep in their sleeping bags and the next day the others would find that the person had turned into some white powder. Not ash, looked more like salt. I was very young when I saw it so can't remember much else.