At least six very young children have been stabbed in a park near Lake Annecy, in France’s south-east, the interior minister says.
Police overpowered and arrested the attacker, Gérald Darmanin said.
Reports say the children were aged about three years old and at least two were in a critical condition.
Regional deputy Antoine Armand described the attack as “abominable” and French prime minister, Élisabeth Borne, is on her way to the scene.
Mr Armand said authorities were investigating and knew “very little”, but his thoughts were with the victims and their loved ones.
The suspect is believed to be a Syrian asylum seeker, according to reports from Le Parisien, BFM TV and AFP quoting police sources.
France’s National Assembly has observed a minute of silence and roads are blocked around the scene of the attack.
President Emmanuel Macron tweeted that the nation was in “shock” and several children and an adult were in a critical condition.