France is bracing for a national day of protests and high-school blockades as a youth protest movement gathers pace amid a growing debate over the scale of the police response.

In one incident, a 15-year-old protesting against what demonstrators said were France’s dilapidated ⁠and understaffed ​schools ‌had his hand ‌blown off outside a high school in the northern town of Lens, said François-Xavier Lauch, the prefect of Pas-de-Calais.

Lauch declined to comment on the exact circumstances, but said between 150 and 200 protesters had been hurling a series of objects at police when riot officers intervened. It was uncertain if the incident had involved a police stun grenade or how the injury happened. Lauch said ​an investigation had ​been opened.

The family of a 16-year-old school pupil in Tours also filed a complaint about police violence after he lost sight in his right eye last week. The state prosecutor said the boy’s injuries were in line with the impact from a police rubber bullet. A police investigation is under way.

The French prime minister, Sébastien Lecornu, had earlier attempted to calm the protests by accepting schoolchildren’s grievances as “legitimate” and saying the government must listen.