Interior Minister Gérald Darmanin said the attack happened at the Gambetta High School in the northern city of Arras at about 11:00 local time.
A teacher has been killed and two people have been seriously injured in a knife attack at a school in France, officials say.
According to witnesses, the killer shouted "Allahu Akbar", or "God is greatest", during the attack, BBC News reports.
Interior Minister Gérald Darmanin said the attack happened at the Gambetta High School in the northern city of Arras at about 11:00 local time.
The attacker has been arrested and is now in custody.
The person killed was a French language teacher while those injured were another teacher and a security guard.
The man, described as being in his 20s, is of Chechen origin and known to the security services for his involvement with radical Islam, according to police.
French media reports say he was a former pupil at the school.
The French anti-terror prosecutor's office says it has opened an investigation following the attack for "murder in connection with a terrorist enterprise" and "attempted murder in connection with a terrorist enterprise".
News channel BFMTV has reported that the brother of the attacker has also been apprehended by police.
Police say the situation is now under control.
French President Emmanuel Macron will visit the school later on Friday, while the National Assembly in Paris has suspended its session in solidarity with the victims.
The attack comes amid rising tensions in France's sizeable Muslim and Jewish communities due to the conflict between Israel and Hamas.
However, police have said there is nothing to indicate a link with the Middle East.
The attack comes nearly three years since the murder and beheading of another teacher, Samuel Paty, at his school outside Paris.
A former leader of Palestinian militant group Hamas Khalid Mashal had called for global jihad on Friday (today), October 13, 2023.
He also called for a show of anger and protests across the Muslim world on Friday in support of Palestinians amid the ongoing conflict with Israel.
Mashal gave the call in a video released on Tuesday in which he asked Muslims worldwide to apply Jihad “on the ground rather than just in theory.”