PARIS — Violence erupted on Saturday in Paris in the 18th weekend of “Yellow Vest” demonstrations as protesters targeted symbols of economic privilege, setting multiple fires and smashing a high-end restaurant on the Champs-Élysées, even as the crowd’s numbers dwindled from past rallies.

Organizers for Saturday’s protests said on social media that they wanted the day to serve as an “ultimatum” to “the government and the powerful.”

The size of the movement that started in November over a proposed gas tax increase and came to embody general discontent against President Emmanuel Macron’s policies has been shrinking from weekend to weekend. But protesters have maintained a continuous presence every Saturday.