New Caledonia has detected three cases of Covid-19 in the community and ordered a two-week lockdown from midday Monday.

The three cases are not connected and involve people who haven't travelled, suggesting the virus is circulating in the community.

President Louis Mapou said investigations have been launched immediately to identify contacts and the chain of transmission.

One of the cases is an unvaccinated person who had already been in hospital in Noumea.

The second infection was picked up in a vaccinated and asymptomatic traveller at a pre-departure check at the international airport in Noumea ahead of a flight to Wallis and Futuna, which has subsequently been cancelled.

The third case is an individual who fell ill on the island of Lifou and was flown to the main island's hospital in Noumea and placed in reanimation.

New Caledonia had its first outbreak in the community in March and managed to eliminate the virus with a month-long lockdown.

With the borders largely closed, anyone arriving must spend two weeks in a government-run quarantine facility.

Last week, the territory's Congress voted to make Covid-19 vaccinations compulsory for adults by the end of the year, triggering a rally on Saturday by thousands opposed to the measure.

Until today, New Caledonia had recorded 136 Covid-19 cases but no fatalities.