A Syrian refugee armed with a knife stabbed four young children and injured two adults by a lake in the French Alps this morning in an attack whose motive remains unclear.

The youngest victim in the quiet town of Annecy was just 22 months old.

Investigators are trying to understand the reasons for the frenzied rampage in a sunny public park at around 9.45am (8.45 Irish time).

All four child victims, including one from the UK and one from Germany, were taken to hospital in a critical condition, along with one of the adults.

The attacker, dressed in black and carrying a blade around 10cm long, could be heard shouting "in the name of Jesus Christ" on a video taken by a bystander and seen by AFP.

"There's no obvious terrorist motive," local prosecutor Line Bonnet-Mathis told reporters in the lakeside town near the Swiss city of Geneva.

She said an investigation for attempted murder had been opened and that the suspect was not under the influence of drugs or alcohol.

Prime Minister Elisabeth Borne said the suspect was "not known by any intelligence service" and did not have "any history of psychiatric problems".

"We are shocked by this hateful, indescribable act," she said after rushing to the scene.

French Prime Minister Elisabeth Borne

Recently divorced and in his early 30s, the suspect had previously lived for ten years in Sweden where he was granted refugee status in April, security sources and his ex-wife told AFP.

"He called me around four months ago. He was living in a church," his ex-wife said on condition of anonymity, saying he had left Sweden because he had been unable to get Swedish nationality.

Ms Borne said he had entered France legally and was carrying Swedish identity documents and a Swedish driving licence.

Interior Minister Gerald Darmanin said France had rejected an asylum request made by the suspect earlier this month, and that he had been carrying "certain Christian religious insignia".

Witnesses described him running around the park on the banks of Lake Annecy wearing a bandana and sunglasses, apparently attacking people at random.

Armed police arrested him at the scene.

Armed police at the scene of the attack in Annecy

"He wanted to attack everyone. I moved away and he lunged at an old man and woman and stabbed the old man," former professional footballer Anthony Le Tallec, who was running in the park, told the local Dauphine Libere newspaper.

A large deployment of security forces cordoned off the park and forensic officers were analysing the scene, an AFP journalist saw.

Locals later returned to the park, with children using the playground.

UK consular officials were travelling to the area to support the boy's family, British Foreign Secretary James Cleverly said during a trip to Paris.

The playground has reopened after the attack

British Prime Minister Rishi Sunak told reporters: "All our thoughts are with those who were affected in this unfathomable attack, including a British child, and their families.

"I have been in touch with President Macron. We stand ready to offer any assistance that we can."

Chancellor Olaf Scholz said "Germany is shocked by this odious and despicable attack in Annecy which also affected a German child."

French President Emmanuel Macron called the violence an "attack of absolute cowardice".

Anthony le Tallec's footage showed police arresting the attacker

France has suffered a series of traumatic attacks in the last decade or so, most of them by Islamic extremists.

In 2012, a Franco-Algerian Islamic extremist named Mohamed Merah killed seven people, including three children and a rabbi at a Jewish school in the southern city of Toulouse.

Most recently, the beheading of a teacher in broad daylight in 2020 near his school in a Paris suburb by a radicalised Chechen refugee led to shock and grief, as well as a national debate about the influence of radical Islam in deprived areas of the country.

Today's attack spurred fresh scrutiny of France's immigration and asylum policy, with right-wing politicians seizing on the culprit's identity as a refugee.

"The investigation will determine what happened, but it seems like the culprit has the same profile that you see often in these attacks," the head of the right-wing Republicans party, Eric Ciotti, told reporters at parliament.

"We need to draw conclusions without being naive, with strength and with a clear mind," he said.