The incident at the Alexis de Tocqueville high school in the town of Grasse provoked shock in France, where such school shootings are rare. The country remains tense and under a state of emergency after deadly Islamic extremist attacks over the past two years.
One student with weapons was arrested, according to a French police official. The official would not elaborate on what weapon or weapons the teenager was carrying.
The government minister for victims affairs, Juliette Meadel, tweeted that two people were wounded and all the students are now safe.
Police cordoned off the area and worried residents gathered outside, along with several emergency vehicles. The town is about 25 miles from the southern city of Nice.
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 metres from the high school, said he had seen about 40 high school students leaving from the area and gathering in a nearby car park.
Both local residents would not provide their names.
The government sent out an alert warning of an attack after police reported that shots were fired. The alert came in a system implemented by the government after the deadly November 2015 attacks in Paris.
Also on Thursday a letter bomb exploded at the French office of the International Monetary Fund, lightly injuring one person, according to Paris police.
Staff from the IMF office were evacuated and armed military officers and police guarded the area, in a chic district of western Paris.
The World Bank office in France is in the same compound.
No other damage was reported in the explosion, according to a police official.
It is unclear who sent the explosive.
Thursday’s incident came a day after a package arrived at the German finance ministry containing low-grade explosives, like those used in firecrackers.
Mail room employees at the ministry quickly identified the package as suspicious and called in explosives experts, who destroyed it with a controlled explosion.
France remains in a state of emergency after a string of deadly Islamic extremist attacks over the past two years.