The woman, who lived in the building, was taken into custody as flames swept rapidly through the block in the French capital's 16th arrondissement, not far from the Parc des Princes stadium, home to the Paris Saint-Germain club.
The Paris prosecutor, Rémy Heitz, said a criminal investigation had been opened. "A person, a woman, who lived in the building has been arrested," Heitz said. He did not confirm reports that residents had heard the suspect involved in a dispute with neighbours.
"At this stage, with what we know, the incident appears to be criminal... this person was arrested in the night not far from the fire... she is in custody," Heitz added. The woman had a history of mental health issues, he said.
Comment: A third fire at a residential block in Paris killed 4, including two children, in late December.