Rain has been battering the remote islands since the weekend, sparking two mudslides in the Houailou area, around 235 kilometres (150 miles) northwest of the capital Noumea, early on Tuesday.
The body of an eight-year-old girl was recovered in mountainous Gouareu, one of two remote communities hardest hit by the disaster. Her injured mother was evacuated and was in a "stable condition", officials said.
A seven-year-old child and a woman in her 30s were also found dead in a nearby area.
The fourth victim was a 60-year-old woman whose body was discovered in Gouareu.
Rescuers, including an army medical team and 30 soldiers, have been deployed to search for those still missing.
All roads, electrical supplies and telephone lines to the area have been cut off and poor weather is hampering rescue efforts.
"The chance of weather conditions improving in the coming hours is not good," the government said in a statement, advising residents to avoid all but essential travel and to take extra care.