Two adults were also injured, both men, one of whom is 78, broadcaster BFMTV has said.

Foreign Secretary James Cleverly confirmed that one of the youngsters is British.

The children include one aged 22 months, two aged two years old and one aged three, according to a local prosecutor.

Two of the children were earlier reported as a brother and sister but BFMTV now report they are cousins.

Update:
What do we know about Annecy knife attacker?

The local prosecutor said another of the children is Dutch, however Germany's chancellor Olaf Scholz said they were German.

One of the injured adults suffered knife wounds and the second was injured both by the attacker's knife and later by a shot fired by police as they were making the arrest.

President Emmanuel Macron said those badly hurt in a park were "between life and death".

A man who spoke to broadcaster BFMTV said he saw first aiders working on "little bodies, three or four years old, perhaps".

A witness who gave his name as Ferdinand told BFMTV: "He (the attacker) jumped (in the playground), started shouting and then went towards the strollers, repeatedly hitting the little ones with a knife."

"Mothers were crying, everybody was running," said George, who owns a nearby restaurant.

A further witness said he saw the attacker assault an elderly man, jumping on him and stabbing him repeatedly. He said he yelled at police to act.

"It's a place where babysitters and parents take young children to play, and the atmosphere is fantastic," said Yohan, who works at an ice cream parlour just opposite the park.

Interior Minister Gerald Darmanin said a suspect had been arrested "thanks to the swift intervention of police".

The perpetrator is a 31-year-old Syrian asylum seeker who carried Swedish identity documents and a Swedish driving license, a police spokesman said.

He entered France legally and was not known to security agencies.

Earlier this month, he had a demand for asylum in France rejected, Mr Darmanin said. He also made asylum requests in Switzerland and Italy.

Line Bonnet-Mathis, the prosecutor of Annecy, said a police firearm was used during his detention, and he was slightly injured.

She said that there was "no apparent terrorist motive" at this stage of the investigation.

The perpetrator has had refugee status in Sweden for the last 10 years, she said.

There is no intelligence on him and no psychiatric report, and he has no fixed abode, Ms Bonnet-Mathis said.

Mr Darmanin said he had certain "Christian religious insignia" on him during the incident.

He is married to a Swedish woman and they have a three-year-old child who was born in Sweden, BFMTV reported.

The couple separated eight months ago and his wife has apparently not heard from him for four months.

He and his wife were studying together to be nurses, BFMTV said.

His motivation is unclear, a source told the Reuters news agency.

Video footage shows two members of the public trying to apprehend him.

BFMTV showed footage of several policemen overpowering an individual in the park.

Former Liverpool footballer, Anthony Le Tallec, said he was jogging around Lake Annecy when he saw the incident unfold.

He commented: "I see that he's (the attacker) heading straight for a group of elderly men and women.

"He attacks one grandpa, stabs him once, the cops can't catch him, so I tell the cops, 'shoot him'.

"Then they start shooting, they shoot at the person, right in front of me, and he falls to the ground."

France attack: What we know about stabbing in Annecy playground

Prime Minister Elisabeth Borne said it was a "heinous, unspeakable act" and the whole country is in "shock".

"Of course, all light will have to be shed. But today is the time for emotion," she said during a press conference.

There is "nothing more abominable than to attack children", French national assembly speaker Yael Braun-Pivet said.

British Prime Minister Rishi Sunak said: "The UK and France have always stood together against acts of violence, and we do so again today."

Speaking during a press conference with US President Joe Biden, Mr Sunak said he has been in touch with President Macron and is "ready to offer any assistance we can".

Francois Astorg, the mayor of Annecy, urged people to avoid the Paquier area of the French alpine town and said his thoughts were with the victims and their families.

In Paris, politicians interrupted a debate to hold a moment of silence for the victims.