The woman and baby as well as three others were injured in the blast in the Mediterranean coastal city of Sanary-sur-Mer, which was heard from as far as eight kilometers (five miles) away.
“It’s very likely that the victim is the father of the baby,” Houda Vernhet, director of the government’s regional authority for the Var region, told AFP.
He was unconscious when located and declared dead after rescue workers spent more than two hours removing him from the unsteady wreckage of the three-story building.
The two people still missing “are a mother, an elderly woman, and her son” who lived on the ground floor, Vernhet said.
“For now, we haven’t yet found any signs of life from the rubble, but we didn’t hear the baby right away, either,” said Col. Eric Grohin, director of the fire service for the Var department.
Authorities said rescue workers smelled gas when they arrived at the site.
“The causes aren’t known for now. There was smell of gas, but we can’t say anything more while the police inquiry is underway,” the regional authorities said in a statement.
Two adjacent buildings were also heavily damaged in the blast that occurred in the port at Sanary, a city of around 15,000 people southeast of Marseille.