The French government sent more police to the Pacific island of New Caledonia on Thursday and said it would crack down on rioters, hoping to restore order after three nights of upheaval in which four people have been killed.

Rioters angry with an electoral reform have burnt businesses, torched cars, looted shops and set up road barricades, causing a "dire situation" for access to medicine and food in the French-ruled Pacific island, authorities said.

"Everything's burning, people have literally no limits," New Caledonia student Olivia Iloa said.

France has declared a state of emergency on the island, put at least 10 people under house arrest and banned TikTok. Numbers of police and gendarmes in New Caledonia will rise from 1,700 to 2,700 by Friday evening, with a small number of soldiers assisting.

"The situation in New Caledonia remains very tense, with looting, riots, fires, attacks which are unbearable," French Prime Minister Gabriel Attal told reporters. France will "show the utmost firmness towards looters and rioters" and toughen sanctions, he said.

Rioting erupted over a new bill, adopted by lawmakers in Paris on Tuesday, that will let French residents who have lived in New Caledonia for 10 years vote in provincial elections. Some local leaders fear the move will dilute the indigenous Kanak vote.

Electoral reform is the latest flashpoint in a decades-long tussle over France's role in the mineral-producing southwest Pacific island some 1,500 km east of Australia.

The government in Paris repeated past mistakes by not heeding warnings over the reform, said Dominique Fochi, secretary general of the Caledonian Union, a branch of the pro-independence FLNKS party which has called for calm but wants the reform shelved.

"We spoke in the void, and now things have exploded," Fochi said.

France annexed New Caledonia in 1853 and gave the colony the status of overseas territory in 1946. New Caledonia is the world's No 3 nickel miner but its nickel industry is in crisis. Economic disparities also fuelled the riots, said Fochi. (Reuters)