The unauthorised march in Noumea was held just a day after the government imposed a limit of 30 people for any outside gathering.
Police say while the meeting was illegal, they didn't intervene because many children were in the crowd.
However, according to the public broadcaster, police used teargas after the end of the rally to disperse some demonstrators.
The march was called to oppose the health pass required to enter venues, such as restaurants and museums, and to protest against the law making vaccinations mandatory.
The law, which is yet to be applied, was adopted last September just days before the territory's delta outbreak, which rapidly infected thousands and killed more than 280.
Last Thursday, first cases of the omicron variant were detected, renewing calls by the authorities to be prudent as the virus is expected to raise infection rates.
From today, vaccinations open for children aged five and older.
Children aged 11 and older must wear masks in indoor settings.
About 65 percent of New Caledonia's population has had at least two jabs, making it the most vaccinated French Pacific territory.
Photo: Clotilde Richalet / Hans Lucas New Caledonia, Noumea. A demonstration against the mandatory vaccination against COVID-19 and against the health pass