Police are blocking streets in the French port of Calais, as extreme left-wing activists are marching and far right activists protest an influx of migrants trying to sneak across the English Channel into Britain.

A few dozen leftists defending the migrants smashed the windows of a car in the city center. One said they were trying to disrupt the demonstration by anti-immigration activists Sunday.

Police barricaded streets and sought to keep the groups apart.

Calais is facing rising tensions over immigration and has about 1,300 migrants from the Horn of Africa, Sudan and Afghanistan. The migrants try to sneak onto trucks or ferries to Britain because they think it is a promised land with generous benefits for refugees — something officials say is a "myth" that must be broken.