Seventeen Africans died and 21 were injured when a blaze ripped through a dilapidated building in Paris early on Friday, the fire service said in a provisional toll.
Among the dead were at least four children, the Interior Ministry said.
The stairwell caught fire from the second to seventh storeys in the building in the 13th district of the French capital.
About 210 firemen from 22 stations were mobilised to fight the inferno, while a criminal investigation was started.
Interior Minister Nicolas Sarkozy was on the scene. Paris Town Hall said Mayor Bertrand Delanoe was on his way back from the southwestern town of La Rochelle.
Residents said the building was occupied by Senegalese and Malians, a hundred of whom would have to be found new homes.