A shocked France is expressing its deep gratitude to a backpacker who put his life on the line to foil a knife-wielding attacker’s rampage through a children’s playground in the mountain town of Annecy.

Two toddlers who were gravely wounded are in a stable condition and doctors are optimistic for their recovery, said President Emmanuel Macron.

Four children in all — aged between 22 and 36 months — and two pensioners were wounded during the assault.

Mr Macron, who has called the attack an “act of absolute cowardice,” visited the hospital in Grenoble where three of the four children are being treated before heading to nearby Annecy.

“The doctors are very confident,” Mr Macron told the police and paramedics who responded to the aftermath of the attack.

Among the children wounded in the attack were a British national and a Dutch national.

A video of the attack, taken by a bystander and verified by Reuters, showed the assailant jump a low wall into a children’s playground and repeatedly lunge at a child in a stroller, pushing aside a woman who tried to fend him off.

‘Unthinkable to do nothing’

France hailed the bravery of a young Catholic pilgrim who came face-to-face with the assailant and used his backpack as a shield as he sought to block the attack.

French media has dubbed the 24-year-old philosophy student, who has identified himself only as Henri, as “the backpack hero”.

“All I know is I was not there by chance,” he told the CNews television network.

“It was unthinkable to do nothing … I followed my instincts and did what I could to protect the weak.”

His Facebook and Instagram accounts were flooded with messages giving thanks for his bravery.

“May God bless you … you did what you could at that moment, you did not give up, you did not run. You are an angel,” Instagram user Mag Capone wrote on his site.

A Mass will be held in Annecy Cathedral in tribute to the victims and their families later on Friday, church authorities said.

Police have arrested a 31-year old Syrian national who was granted asylum in Sweden 10 years ago, Borne said on Friday.

He had entered France legally, she said, and was carrying Swedish identity documents and a Swedish driving licence.

Sweden and France are both members of the Schengen Area, the world’s largest passport-free zone which allows the unrestricted movement of people between 26 European countries.

The attack has laid bare the tensions between Europe’s free movement rights and the pressure governments in countries like France and Italy are coming under from voters to toughen immigration laws as societies shift rightwards politically.

One of the two pensioners caught up in the attack told Reuters he had been sitting on a park bench when the attacker approached on the run.

“He probably wanted to create one more victim,” said Youssouf, who asked his family name not be published..

-AAP