Protesters march during a nationwide blockade by high school students in Marseille. (AFP pic)

PARIS: Tens of thousands of demonstrators are expected on the streets of Paris on Tuesday as France's powerful trade unions join high school students rallying for better conditions in a wave of protests marked by clashes with police.

Students have blocked the entrances to hundreds of high schools for 15 to 17-year-olds since late September, complaining of missing teachers, overloaded timetables, dilapidated classrooms and buildings that cannot cope with rising temperatures.

While many protests have been peaceful, some students have lit dustbin fires, torched bus shelters or clashed with riot police, who have responded with batons, tear gas and riot-control rounds.