France has offered citizenship to an immigrant from Mali who climbed four storeys up a Paris apartment block to save a boy who was about to fall from a balcony, President Emmanuel Macron says.

Key points: According to the French news station La Chaîne Info, the child had been left alone while his father went shopping

According to the French news station La Chaîne Info, the child had been left alone while his father went shopping The 22-year-old is a Malian immigrant, who said he arrived a few months ago

The 22-year-old is a Malian immigrant, who said he arrived a few months ago Mr Gassama has even been invited to the Elysee presidential palace to meet with President Emmanuel Macron

Incredible footage emerged yesterday showing 22-year-old Mamoudou Gassama risking his life on Sunday as he climbed up the balconies to rescue the four-year-old who is clinging to a railing and glancing at the ground below, while horrified onlookers watched.

Mr Gassama reached the boy within minutes, prompting a loud cheer from the crowd below.

The video went viral and Mr Gassama, who has been nicknamed "Spider-Man" for reaching the boy in the nick of time, was swiftly granted a meeting at the Elysee Palace.

"I did it because it was a child," French newspaper Le Parisien quoted Gassama as saying.

"I climbed … thank God I saved him."

The boy's father was later arrested and told police he had left his son alone to go shopping and returned home later than planned because he was playing Pokemon Go, an enhanced reality game, on his smartphone.

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"Bravo," Mr Macron said to Mr Gassama during a one-on-one meeting in a gilded room of the Elysee Palace that ended with the awarding of a medal from the prefecture for "courage and devotion".

Mr Gassama, dressed in blue jeans and white shirt, recounted his experience when he and friends saw the young child hanging.

"I ran. I crossed the street to save him," he told Mr Macron during a filmed portion of the meeting. He said he didn't think twice.

"When I started to climb, it gave me courage to keep climbing."

Mr Gassama felt fear when he took the child into the apartment. "I was trembling," he told Mr Macron.

Mr Macron congratulated Mr Gassama for "an exceptional act" and said France would give him a job in the emergency services.

"We'll obviously be setting all your papers straight and if you wish it, we will start the process of naturalisation so that you can become French," he said.

"What you have done corresponds with what firefighters do; if this fits your wishes, you could join the firefighters' corps so that you can do [such acts] on a daily basis."

Ministers said the citizenship process would be sped up, although Mr Gassama cannot legally be granted it right away.

The French President suggested Mr Gassama become a firefighter. ( AP: Thibault Camus, Pool )

'Spider-Man's' act praised in home country

Adam Thiam, a Malian analyst and former presidential advisor, told Reuters that Mr Gassama's act had been praised in his home country.

"There is great pride here in Mali," Mr Thiam said.

"But while [Mr Gassama] gets the honours, there are … Malian citizens under the threat of being expelled by the French Government."

Mr Gassama told Paris Mayor Anne Hidalgo by phone on Sunday he arrived from Mali a few months ago and wished to stay in France.

"I replied that his heroic gesture was an example for all citizens and that the City of Paris will obviously be keen to support him in his efforts to settle in France," Ms Hidalgo said.

Mr Gassama told Mr Macron that he arrived in Italy in 2014 after more than a year in Libya, where he was arrested and beaten, "but I wasn't discouraged".

The French President is toughening the nation's approach to immigration, and stressed that not all who make the treacherous journey to Europe can be welcomed, but that Mr Gassama's actions were admirable.

"You saved a child. Without you, no one knows what would have become of him," Mr Macron said.

"You need courage and the capability to do that.

"You have become an example because millions have seen you [on social media]."

ABC/Reuters