The four-storey house collapsed in the centre of the southern port city shortly after midnight. Parts of two neighbouring houses were also brought down in the overnight collapse.
At least five people were injured, initial information showed. According to media reports, they were in a neighbouring building.
The destruction was likely caused by an explosion, but authorities do not have a cause yet.
"We cannot know today what caused this very big explosion," said Interior Minister Gerald Darmanin. In any case, the house was not known to be in danger of collapsing.
"We think there are between four and 10 people under the rubble," Darmanin said on Sunday. Some 30 homes were evacuated as a precaution, he said.
It is unclear exactly how many people were in the building that initially collapsed.
"Four people seem to have been in the building for sure," said Darmanin, who travelled on Sunday morning to the scene of the accident. "We don't know if they are alive or dead."
Marseille Mayor Benoit Payan stressed that the search for possible survivors was the absolute priority.
But rescue efforts are proving difficult. Shortly after the house collapsed, a fire ignited under the rubble and was still burning at midday on Sunday.
"We are facing a very rare phenomenon - a fire that has been going on for several hours with extremely high temperatures," Payan said. Darmanin said the debris virtually covered the entire fire.
"You can't proceed in a very classical way, because if there should be survivors, of course the water or foam that the firefighters use must not prevent them from surviving."
The fire is also a problem for the rescue dogs deployed. Because of the fire's smell and the hot temperatures, they have not been able to search for buried people. The dogs did not find any human traces at first, Payan said.
"That doesn't mean anything. We can't draw any conclusions at this moment."
The incident in the early hours of Easter Sunday triggered reactions of shock and horror from neighbouring residents interviewed by the broadcaster BFMTV. They spoke of hearing a loud bang and screams.
French President Emmanuel Macron wrote on Twitter that he was moved and was thinking of all those affected and their families. Prime Minister Elisabeth Borne also expressed her concern on Twitter.
