French firefighters evacuate a woman near the Tocqueville high school after a shooting incident injuring at least eight people, in Grasse, southern France, March 16, 2017. [Photo/Agencies]

The incident in Grasse, which does not appear to be linked to militancy, comes with France on high alert after more than 230 people were killed in the past two years by attackers allied to Islamic State.

"It was total panic," Achraf, a student in the school, said on BFM TV. "The gunshots were at 4 to 5 metres from where we were. We thought the gunman was coming towards us. We heard him shouting."

France's Education Minister Najat Vallaud-Belkacem visited the scene in Grasse, a town known for its perfume industry, and said the attack appeared to be "a crazy act by a fragile young man fascinated by firearms".

"His motivations seem to be linked to bad relations he had with other students in school," Grasse prosecutor Fabienne Atzori told reporters.

With a presidential election less than six weeks away, the attack by a 16-year-old armed with a shotgun loaded with lead pellets looked likely to further stoke France's debate on security.

Separately in Paris, an employee of the International Monetary Fund (IMF) was injured in the face and arms when a letter bomb posted to the world lender's local office blew up as she opened it, police said.

Atzori said 10 people had been hurt in the school attack, either physically or emotionally. One person was shot in the stomach and the headmaster was injured in the shoulder after trying to stop the gunman.

The youth, who was also carrying munitions, handguns, a grenade and what seemed to be a homemade explosive device, put up no resistance when he was arrested at the school, she said.

The youth was not known to police and checks were being made to establish whether there were any accomplices and how he had acquired his weapons.

"The first investigations suggest he had consulted videos of mass killings in America," an interior ministry spokesman said.