A high school student was killed and three others were injured in a knife attack at a school in the western French city of Nantes on Thursday before the assailant was overpowered by teachers, police said.

BFM TV reported that the student who was killed was a girl. Police did not confirm the age or gender of the victim.

The attacker, aged 15, was overpowered by teachers at the Notre-Dame-de-Toutes-Aides private school before police arrived, a police spokesperson said.

She said there was nohting pointing to a terrorist motive.

French broadcaster franceinfo reported that the stabbing followed a conflict among students and that the attacker had suffered from depression.

Local newspaper Ouest France said the attacker was dressed all in black, and wore a helmet and balaclava. Two knives were found lying next to the assailant's belongings, it said.

BFM reported that the attacker had emailed a document to all students in the school which painted a bleak picture of society. Police could not immediately confirm the report.