Local authorities quoted by French media said the boy's parents were not at home at the time.

The father has been questioned by police on suspicion of leaving his child unattended, judicial sources say. The mother was not in Paris at the time, it is believed.

Paris Mayor Anne Hidalgo was among those to praise the 22-year-old's heroism and said she had called him to thank him.

She referred to him as the "Spiderman of the 18th", referring to the Paris district where the rescue took place, calling him an "example for all citizens".

France's new Malian hero

Alex Duval Smith, West Africa correspondent, BBC News

Mr Gassama's four-storey dash is a reminder of another Malian hero who gained national prominence in January 2015 during an extremist attack on a Jewish supermarket in Paris.

A young Malian employee, Lassana Bathily, was credited with saving the lives of six hostages including a baby when he led them to a safe hiding place, escaped, then directed gendarmes to their rescue.

Two weeks later - after six years of struggling to secure legal residency in France - Mr Bathily was given a medal and a French passport by then President François Hollande.

In 2016, he wrote a book ''Je ne suis pas un heros'' (I am no hero) and created a charity whose first project was to provide irrigation for his home village in western Mali.

Like Mr Bathily's selfless leadership to save the hostages, Mr Gassama's heroic climb to save the boy cements the image of Mali as a country with a culture of old-fashioned public spiritedness.