Home Affairs Minister Gerald Dormanin said the victims included three young children and that “police will shed light on the circumstances of this horrific tragedy”.
The fire on the second floor spread to the upper floors. Good attorney Damian Martinelli told reporters that in light of the preliminary findings, “I have opened an investigation into the arson that caused the death.”
According to local reports, all the seven victims belong to the same family. Officials said three adults, a teenage girl and small children aged five, seven and 10 died.
Two members of the family reportedly tried to escape through a window – one died and the other is in critical condition.
Prefect Hughes Mouto said everyone was affected by the tragedy and was “very committed to providing help and assistance to the survivors”.
A man identified as Iftahou told the Nice Met website that he arrived at the scene while the fire was still burning and realized there was no hope for those inside.
Nazim Mecha, head of the Comorian community in the south of France, said he knew the family and that they had been living in Nice since around 2013.
Nice Mayor Christian Estrozzi said the toll of the disaster was too high. Along with the seven victims, 30 others suffered smoke inhalation.
“I have asked the interior minister to deploy security forces to ensure the safety of residents and avoid fresh incidents after this tragedy, which is being investigated as arson,” he said.
President Emmanuel Macron, who is visiting England, said: “Our thoughts are with the relatives of the victims. We are with them and with the people of Nice.”