Seven wounded in Paris knife rampage as petanque players try to disarm attacker by pelting him with boules

French police on Monday opened a case of attempted murder after a man injured seven people in a knife attack in central Paris late on Sunday.

Four of the victims were in a critical condition, police said. Two British tourists are among the injured.

Bystanders tried to stop the attack by throwing petanque balls at the man, who was brandishing a large blade and an iron bar.

The attacker is believed to be an Afghan national and has been arrested, according to a judicial source. The man is said to have targeted "strangers", but "nothing at this stage shows signs of a terrorist nature".

The attack took place on the banks of the Bassin de la Villette just after 11pm. The area is popular with locals and tourists, who frequent the cafes, cinemas and other cultural venues.

Witness Youssef Najah, 28, said he was walking beside the canal when he saw a man running and holding a knife about 25-30 centimetres in length.

"There were around 20 people chasing him. They started throwing petanque balls at him," Mr Najah said, referring to the sport popular in France, also known as boules, played with hollow steel balls.

"Around four or five balls hit him in the head, but they weren't able to stop him," he said.

The attacker then fled into an alleyway, where he "tried to hide behind two British tourists", he said.

"We said to them: 'Watch out, he has a knife.' But they didn't react".

The pair were then attacked, he said.

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A cinema security guard said he saw the attacker running away from two men who were trying to stop him.

"He had an iron bar in his hand which he threw at the men chasing him, then he took out a knife," he told AFP.

The UK Foreign Office said it was "urgently investigating this incident" in co-operation with French authorities, British media reported.

High alert

A judicial source said a police investigation was under way for attempted murder.

It is the latest in a series of knife attacks in France in recent months, with terrorism being ruled out in most cases.

On August 23, a man stabbed his mother and sister to death and seriously injured another person in a town near Paris before being shot dead by police.

The motive for the violence remained unclear despite a claim by ISIS that it was an attack by one of its fighters responding to the terror organisation's propaganda.

Authorities said the 36-year-old had serious mental health problems and had been on a terror watch list since 2016.

That attack came days after an Afghan asylum seeker was arrested in the town of Perigueux for a drunken rampage with a knife in which four people were wounded, one seriously.

Police said investigators "very quickly" dismissed a terrorist motive after the August 13 incident.

And on June 17, two people were hurt in another southern town when a woman shouting "Allahu Akbar" (God is greatest) attacked them in a supermarket with a boxcutter knife.

France has been on high alert following a series of extremist attacks in recent years, often by people who have become radicalised or claim to have acted in the name of ISIS.

More than 240 people have been killed by extremists since the massacre at the Charlie Hebdo satirical magazine in Paris in January 2015.