New Caledonia will go into a two-week lockdown from midnight after nine Covid-19 cases were confirmed in the community.
The measure was announced a day after neighbouring Wallis and Futuna reported its first Covid-19 case in the community.
The source of the outbreak in Noumea had not been established but it is believed to be linked to the emergence of Covid-19 in Wallis and Futuna.
Passenger flights between the two territories have been suspended and internal flights in New Caledonia as well as flights between Wallis and Futuna are being stopped.
The New Caledonian government has asked anyone who arrived from Wallis and Futuna since 25 January to isolate and contact the health authorities.
The French prefect in Wallis and Futuna said the first case was detected in a school principal who weeks ago had been allowed to leave quarantine after returning negative Covid-19 tests.
The individual fell ill and tested positive for the coronavirus, with reports saying he may have to be evacuated to Noumea.
In New Caledonia, schools and businesses will close.
Anyone in public will be required to carry an attestation justifying their movement.
In New Caledonia, just over 5,000 people have been vaccinated while in Wallis and Futuna an inoculation programme is about to be rolled out.
In Wallis and Futuna, where yesterday another six Covid-19 cases were detected, there is no plan to order a lockdown but the wearing of masks in public places is mandatory.