Protesting student teachers from a rural training college in Michoacán clashed with state police officers on Monday.
The students tried to stop trucks and buses on the Siglo 21 highway near Tiripetío, 25 kilometers southwest of Morelia, in order to block traffic.
When state police arrived, the protesters fired rockets and threw stones at them.
In response, the officers fired tear gas at the students, who fled to their nearby school.
In a video published by the news website La Silla Rota, some 100 protesters are seen on both sides of the highway with a large cloud of gas spreading across it.
The Public Security Ministry said that there were no injuries.
The students were demanding that jobs be automatically awarded to teachers who have completed their training, without fulfilling the legally required accreditation process. It is a perennial demand by students and the dissident CNTE teachers union.
Blockades are a common tactic for dissatisfied teachers and teachers-to-be in Michoacán and other states: members of the CNTE blocked tracks for 91 days last year, costing businesses an estimated 50 million pesos per day (US $2.5 million at the exchange rate at the time).