Located on the banks of the Vesdre river, near Liege, the plant produces more than 1,700 tonnes of chocolate a year to customers all over the world, including Belgium’s royal family.
Local reports suggest the factory has ground to a halt after a week of torrential rains swept through production lines, damaging machines and destroying ingredients.
"The priority now is to secure the factory and to get the electricity back on," spokesperson Valerie Stefenatto, told local media.
Galler chocolate is one of Belgium’s iconic luxury chocolate brands.
Vats of raw ingredients had been damaged in the floods and locals report the smell of chocolate in the air.
When the river level started to rise last Wednesday, staff stacked sandbags and shut off production, but were engulfed on Thursday after unprecedented rainfall that has killed at least 190 people, including five residents in Liege.
Hundreds of Belgians have also been left homeless because of flood damage to their property.
"The factory has been here since 1976. We've never known a flood in Vaux-sous-Chevremont," said Stefenatto.