Dozens of hooded anarchists have clashed with riot police blocking their approach to the Austrian border during a protest against plans to tighten border controls to prevent the passage of migrants.

Riot police just hundreds of meters (yards) from Italy's northern border responded Saturday with tear gas after anarchists who also came with helmets and gas masks threw objects including bricks and firecrackers at police blockade. Italian RAI state television cameras showed police detaining one demonstrator near train tracks.

The protest spilled over on to the railway, blocking service, and then onto the highway.

The demonstrations come after Austria announced moves to tighten surveillance of the border out of concern that the flow of migrants to northern Europe will shift to Italy after the closure of the Balkans route.