Prime Minister Jean-Marc Ayrault announced the emergency during a visit to the town of La Londe-les-Maures, Radio France Internationale reported.
In La Londe-les-Maures, a 70-year-old man died when he was trapped in the cellar of his home by floodwaters that affected about 600 area residents.
Another man died when his vehicle was swept away on a flooded road.
Ayrault said a "huge effort" was being made to "reconstruct" the area.
"We'll come to the rescue, that's what we're here for," he said.
Authorities deployed emergency helicopters, 500 firefighters and 200 police to Var overnight to help people in the area.