The Parks and Recreation star, 50, and his teenage son Johnny both posted dramatic images online showing the home's first floor being swept through by muddied waters from torrential overnight storms.
"This is right outside the house. Was twice as high at the worst, just before sunrise," Lowe wrote on Instagram.
Johnny posted a video on Instagram showing the floodwaters pouring through. "That's the first floor of our house submerged. Scariest hour or so of my life," he wrote.
Johnny later posted a photo of the scene on Twitter, writing: "Thank you to the fireman that saved us from this nightmare. Happy for us all to be safe, thoughts to others."
Local officials told PEOPLE that low-lying areas were under as much as 5 feet of water. "This was the biggest storm of the year," one rescue official said. "Water rising like that can be terrifying. There's only one rescue station in Grasse, and this storm required assistance from several other regional units. We were called out on a lot of emergency rescues yesterday."
As much rain fell in four hours as usually falls in four months, locals tell PEOPLE, causing mudslides, road washouts and power outages.
Lowe also posted an Instagram photo, later apparently deleted, showing his wife Sheryl Berkoff hugging a fireman. "My wife," he wrote, "being rescued this am in the horrific flooding in Grasse France. Glad we are safe. Grateful to first responders."
The family's rescue comes amid an extended European vacation, with stops in London, Cannes and Spain, to celebrate Johnny's high school graduation. On Tuesday, Lowe had lunch at a neighboring Saint-Paul-de-Vence restaurant alongside actor Roger Moore.