People in Vanuatu are being urged to get in touch with the authorities if they see Vietnamese "blue boats" in local waters.
The Director of the Fisheries Department, Kalo Pakoa, said people should report any sighting or other information to the department or the police.
The illegal and unregulatedboats have been caught in several countries and territories over the past few years including Palau, the Federated States of Micronesia, Papua New Guinea, Indonesia, Australia and this week in New Caledonia.
Mr Pakoa said boats caught fishing illegally in New Caledonian waters were in Vanuatu's Exclusive Economic Zone and they could be on any remote reef at the moment.
He said the boats didn't have a valid fishing license from any government including the Vanuatu government and he said they were a threat to Vanuatu coastal waters.
The French military, this week, launched an operation to catch two of the small blue-painted wooden boats which escaped from New Caledonia custody.