A suspected knifeman has been arrested after several very young children – including one in a pushchair – were stabbed in a lakeside park in the French Alps.
Adults were also attacked in the town of Annecy on Thursday.
At least two children and one adult have been left with life-threatening injuries, authorities said.
One of the injured children is British, UK Foreign Secretary James Cleverly said.
He said: “Our thoughts are with the victims and the families and we stand ready to support the French authorities in whichever way we can.
Mr Cleverly said he was “also aware that one of the people, one of the children injured, was a British national”.
“And of course we stand in strong solidarity with the people of France at this terrible time.”
Video on social media appeared to show the attack in a children’s play park.
Footage showed a man in dark glasses and with a blue scarf covering his head brandishing a blade as people screamed for help.
He slashed at a man carrying rucksacks who tried to approach him, seemingly trying to stop the attack.
Inside the enclosed play area, a panicked woman frantically pushed a pushchair as the attacker approached, shouting for help and ramming the pushchair into the park’s barriers in her terror.
She tried to fend off the attacker but could not stop him from leaning over the pushchair and stabbing downwards repeatedly.
The man strolled almost casually out of the park, letting himself out through a gate, with the man carrying two rucksacks still chasing after him.
French President Emmanuel Macron described the attack as one of “absolute cowardice”.
“The nation is in shock,” he tweeted.
Local police said the four child victims are all under the age of five.
National police said two of the children, both about three, suffered life-threatening injuries, as did one adult.
The witness said he shouted at police to act.
An ice cream seller who works in the waterside park said he had seen the alleged attacker there several days earlier, looking out at the lake ringed by mountains.
Local police said a second adult was hurt and was being treated with the others in hospital.
They gave no other details about the victim and the discrepancy in the number of adult victims was not immediately explained.
The attack happened near a primary school, he said.
In Paris, politicians interrupted a debate to hold a moment of silence for the victims.
Assembly president Yael Braun-Pivet said: “There are some very young children who are in critical condition and I invite you to respect a minute of silence for them, for their families, and so that, we hope, the consequences of this very grave attack do not lead to the nation grieving.”