French President Emmanuel Macron was on his way to the attacked school when the anti-terrorism prosecutor's office said it had opened an investigation into the incident.
The attack occurred at around 11 am. BFM reported that the person killed was a French literature teacher. A sports teacher and a security guard were also seriously injured and hospitalized, according to police.
Footage taken by students and shared on social media shows a man in a gray jacket walking with a knife and attacking people in the school courtyard. One person tried to keep the attacker away using a chair.
Police said the incident was under control and there was no danger.