A young man from Africa climbed out of obscurity and into the hearts of Europeans on the weekend when he leapt into action to save a toddler who had been dangling from a Paris balcony.

Mamoudou Gassama, an immigrant from Mali, saw a crowd of onlookers staring up at the 4-year-old and sprang into action, clambering up the outside of the building and grabbing the terrified boy just in time.

His quick response, bravery, and agility instantly won him praise and legions of fans, with Anne Hidalgo, the city's mayor, thanking the 22-year-old personally and dubbing him the "Spiderman of the 18th" in reference to the North Paris district where the incident happened on Saturday evening.

The BBC said Hidalgo cited him as an "example for all citizens".

And French President Emmanuel Macron thanked him on Monday at Elysee Palace, saying he will be made a naturalized French citizen. The broadcaster said Macron also presented Gassama with a medal recognizing his courage, and said he will be offered a role with the fire department.

Gassama told French broadcaster BFMTV he acted spontaneously.

"I did not think, I saved him," he said. "When I took him in my arms, I spoke with him and asked: 'Why did you do that?' But he did not answer."

AFP noted that fire crews arrived to find the boy had already been saved.

"Luckily, there was someone who was physically fit and who had the courage to go and get the child," a fire department spokesman said.

The Guardian newspaper said the boy's mother was not in Paris at the time and noted his father had been questioned on suspicion of leaving the toddler home alone.

The newspaper added that the enormity of the situation only dawned on Gassama after the rescue was over.

"I felt afraid when I saved the child," the paper quoted him as saying. "We went into the living room. I started to shake. I could hardly stand up, I had to sit down."

Hidalgo said Gassama had not been in the country for long.

"He explained to me that he had arrived from Mali a few months ago, dreaming of building his life here," she said. "I told him that his heroic act is an example to all citizens and that the city of Paris will obviously be very keen to support him in his efforts to settle in France."