An intruder burst into the Tocqueville high school and opened fire, one of the sources said.

Eight people were injured after a shooting at a high school in the small southern French town of Grasse, the interior ministry said, and a 17-year old student carrying a rifle, handguns and grenades was arrested, police sources added.

“The individual does not seem to be known by police,” one source said.

A second source said it appeared that two students had opened fire on the headmaster, who had been injured, adding that the suspects did not seem to be militants.

“One of the two was arrested and the second fled. There was panic and the students took refuge in the (neighbouring) supermarket,” said the source.

Another police source it was not yet possible to confirm if there was a second shooter.

Interior ministry spokesman Pierre-Henry Brandet told BFM TV that eight people had been injured, and advised families to remain patient as police took control to stabilise the situation.

All schools in the town some 40 kilometres (25 miles) west of Nice have been locked down, education authorities said.

A crisis cell has been put in place after the attack at the high school, education official Emmanuel Ethis said on Twitter.

French television BFM showed residents gathered around the area, along with several police cars and emergency vehicles. Residents said some students have been able to leave the school.

An employee of a nearby electronics store said police had asked residents to stay indoors. An employee of sports chain Decathlon, which has a branch less than 500 meters from the high school, said he’d seen about 40 high school students leaving from the area and gathering in a nearby parking lot.

Interior Minister Bernard Cazeneuve cut short a trip to the northern Somme area because of the Grasse shooting, as well as a letter bomb blast at the offices of the International Monetary Fund in Paris on Thursday.

A letter exploded Thursday at the French office of the IMF, lightly injuring one person, amid heightened security around Europe after a string of deadly attacks.

The incident came as a Greek anarchist group claimed responsibility for a failed letter bomb sent to the German Finance Ministry on Wednesday.

After Thursday’s explosion in Paris, staff from the IMF office were evacuated and armed military officers and police guarded the area, in a chic district of western Paris.