According to the public broadcaster, a French surveillance aircraft spotted two boats near Ouvea after which a naval vessel intercepted them to escort them to Noumea.
Reports said a Vietnamese fisherman, who was in a serious condition after a suspected diving accident, was immediately taken off and flown by helicopter to hospital.
Two other blue boats were seen near Belep and the navy succeeded in catching one of them.
A week earlier, French surveillance teams helped Solomon Islands catch three blue boats fishing illegally.
Three Vietnamese captains caught in New Caledonia this year are serving jail sentences.
The Forum Fisheries Agency said the large numbers of Vietnamse blue boats should be labelled reef robbers for their persistent illegal activities around Melanesian islands.
Photo: AFP A Vietnamese "blue boat".