Police attended Saint-Thomas d'Aquin school with the local prosecutor, where the student was arrested.

French newspaper Sud Ouest said the attacker entered the classroom while the Spanish teacher was giving a class and attacked her.

The teacher was in her fifties and died of cardiac arrest after emergency services arrived at the school, local media reported. French TV station BFM said the attacker locked the classroom door and stabbed the teacher in her chest.

France's Education Minister, Pap Ndiaye said in a tweet that his thoughts were with the teacher's "family, colleagues and pupils".

He said he was on his way to the school "straight away". Local media reported the student may have been suffering from mental health issues. They said at this stage of the investigation there was no suggestion the incident was terror-related.

In a press conference, Mr Véran said the government would support educators across the country in the wake of the incident.

"I can hardly imagine the trauma that this represents," he said.

The school is a private, Catholic establishment near the centre of Saint-Jean-de-Luz, a well-known French summer holiday location.