French teenagers kept up blockades at high schools on Thursday after the prime minister promised action on their grievances but offered no specifics.

The education ministry said 224 high schools were closed on Thursday morning, while 151 were partially reopening after earlier closures. It said closures had fallen 30 per cent from Wednesday and that 94 per cent of high schools were fully or partially open.

The movement is now into its third week. Students are demanding action on teacher shortages and crumbling school buildings. The protests have led to hundreds of arrests and dozens of injuries, and the government has suspended the use of stun grenades in policing the demonstrations.

Prime Minister Sebastien Lecornu pledged "concrete, quick and fully funded responses" by late October but gave no details. Unions are already planning a bigger day of protests on October 17.

The unrest has exposed a deeper tension: students want investment in deteriorating public services while a cash-strapped government faces pressure from bond markets to cut debt. France's 10-year bond yield briefly topped 5 per cent last week, a 24-year high.