They say the individual, who had arrived from French Polynesia, has been transferred to the dedicated COVID-19 isolation unit of the main hospital in Noumea.
New Caledonia has been COVID-free since it succeeded to suppress a community outbreak in March with a month-long lockdown.
A government statement said the latest discovery doesn't call into question the need for everyone to be vaccinated to limit the spread of the virus.
With the border largely sealed, all arriving people have had to go into managed isolation for two weeks, but the stay has been shortened to one week for those who are fully vaccinated.
Photo file RNZ