PARIS, Oct 16 — After weeks of student protests, France is set to be swept by broader, nationwide demonstrations Saturday over the cost of living, setting up a potentially fraught period ahead of presidential elections next year.

The prospect of the two movements merging, perhaps with outbreaks of violence, poses a big challenge to the government — and an opportunity for far-left and far-right presidential candidates jockeying for power.

The country’s Yellow Vest movement, which eight years ago staged street protests against President Emmanuel Macron and his government, called Saturday’s “yellow and youth” demonstrations and urged millions to turn out.

It has appealed to teachers, workers, pensioners and farmers, as well as students, in an online call spread through social media.