A pro-independence activist in New Caledonia is warning France to immediately halt planned constitution amendments or face "war".

The call for a u-turn follows proposed constitutional changes to voting rights which could push the number of eligible anti-independence voters up.

Pacific Independence Movement (le Mouvement des Océaniens indépendantistes) spokesperson Arnaud Chollet-Léakava was one of the thousands who took to the streets in Nouméa in protest on Saturday (local time).

He told RNZ Pacific that tensions were high.

"We are here to tell them we must not make this mistake," Chollet-Léakava said.

"Step by step, I think there will be war."

A nearby counter-protest in Nouméa also had a large turnout.

People there wore the French flag, a contrast to the sea of blue, red, green and yellow representing the Kanak flag at the pro-independence rally.

Solange Ponija was one of thousands at the pro-independence rally in Nouméa.

The constitutional change - if pushed through - will tip the balance of voting power onto the French side, she said.

She feared the indigenous people of New Caledonia, Kanak peoples, will lose in their fight for independence:

"They want to make us a minority... it will make us a minority!

"The law will make the Kanaky people a minority because it will open the electoral body to other people who are not Kanaky and who will give their opinion on the accession of Caledonia to full sovereignty," Ponija said.

A French man who has lived in New Caledonia for two decades said independence or not, he just wanted peace.

The man - who wanted to remain anonymous out of fear of retribution - said he moved to New Caledonia knowing he would be living on colonised land.

Having experienced violence in 2019, the man begged both sides to be amicable.

"[It's] very complicated and very serious because if the law is not withdrawn and passed. We are clearly heading towards a civil war.

"We hope for peace and we hope that we find a common agreement for both parties.

"People want peace and we don't want to move towards war," the man explained.

The constitutional bill was endorsed by the French Senate on 2 April.

The next stage is for the bill to be debated, which has been set down for 13 May.

Then both the Senate and the National Assembly will gather in June to give the final stamp of approval.

This would allow any citizen who has lived in New Caledonia for at least 10 years to cast their vote at local elections.

- RNZ