Demonstrators in the Mexican capital hurled rocks and projectiles at riot police, who responded by firing teargas to disperse the angry crowd.
Police presence grew heavier as thousands of protesters took the streets chanting and raising their fists.
The violence marks the anniversary of the Tlatelolco massacre in the capital. In 1968 security forces stormed a leftiest student rally in Mexico City's Tlatelolco district, killing 30-40 people, according to officials, or as many as 300, according to rights activists and witnesses.
The killings took place just days before the Olympic Games in the capital, as the government tried to quell weeks of what it saw as embarrassing demonstrations by students demanding democratic reforms in authoritarian Mexico.