A chocolate factory and a soda bottling plant set on fire. Molotov cocktails thrown at the police, and prisoners taking guards hostage. Five people dead. As protests against French control boiled over this week in New Caledonia, the South Pacific archipelago experienced some of its most intense violence since a civil war decades ago.

“I’m in a state of shock, I can’t move,” Lizzie Carboni, a writer who lives in Noumea, the capital, said by phone as the fourth night of protests began on Thursday. When she checked on her parents, Ms. Carboni said that her mother told her: “We never wanted to tell you about what happened in 1984, but it’s happening again.”

France annexed New Caledonia, which lies about 900 miles off the eastern coast of Australia, in 1853. It built a penal colony and over time shipped in more foreigners to mine New Caledonia’s vast nickel reserves. That eventually made the Indigenous Kanaks a minority in their own land.

The most serious challenge to French rule came in the 1980s, when French troops were ordered in to quell a violent uprising. Dozens of people died in the ensuing clashes. To end the fighting, French authorities agreed to put New Caledonia on a pathway to independence.

But the calculus in France has changed in recent years with the intensification of the jostling between the United States and China for influence in the Pacific. French officials fear that China could gain sway in an independent New Caledonia, just as it has sought to do in other South Pacific countries like Vanuatu and the Solomon Islands.

President Emmanuel Macron of France visited New Caledonia last July and laid out his vision for the Pacific outpost.

“New Caledonia is French because it has chosen to remain French,” Mr. Macron told a crowd of people opposed to independence. “No going back. No stuttering.”

Four decades after the civil war ended, however, pro-independence sentiment and resentment against French settlers remain strong in New Caledonia, which is now semiautonomous.

In the 1980s, France agreed to hold an independence referendum within a decade — a bet that a rising Kanak middle class would choose to remain French. As the new century dawned, voting was put off for two more decades. But the French authorities agreed to freeze electoral rolls so that recent arrivals to New Caledonia, who are thought to be more likely to support continued French rule, would not sway the vote. France also agreed to hold three referendums instead of one, a nod to the possibility of violent protests.

In the first, held in 2018, the pro-independence camp had a surprisingly strong showing, garnering 43 percent of the vote despite concerns that New Caledonia’s beleaguered nickel-dependent economy could not survive without financial assistance from France. Two years later, 47 percent voted for independence.

The third and last referendum took place after the coronavirus pandemic, which devastated many Kanak communities. Local mourning customs prohibit political activity, and Indigenous leaders urged Mr. Macron to delay the 2021 vote. When it went forward as scheduled, many Kanaks boycotted it in protest, and the vote was overwhelmingly in favor of staying with France.

Pro-independence leaders have called for holding another vote, but talks with French authorities are at an impasse. And Mr. Macron’s government has backed an amendment to the French Constitution that would allow some people who have moved to New Caledonia since 1998 to vote in the territory, calling it a move toward full democracy.

While pro-independence sentiment is longstanding in New Caledonia, the most recent string of demonstrations began on May 4 with a commemoration of the death of Jean-Marie Tjibaou, a Kanak leader who was assassinated by a disaffected nationalist after negotiating the end to the civil war. Protests spread across the 140 islands of New Caledonia, which is home to about 270,000 people.

In an interview last year, Mr. Tjibaou’s son Joël Tjibaou said that France did not understand the depth of feeling in the country.

“When you see our country, you understand why we are fighting for independence,” he said. “The white people came here, stole our land, stole our customs, don’t respect us.”

On Monday, France’s lower house of Parliament debated the constitutional amendment, which has already been passed by the Senate. As it became clear that the proposal would pass, protests in New Caledonia, especially those in Noumea, turned violent, according to Adrian Muckle, who teaches history at Victoria University of Wellington in New Zealand.

“We are in a state of civil war,” Sonia Backès, the territory’s most prominent anti-independence politician, wrote to French president Emmanuel Macron on Wednesday. “Without massive and urgent intervention from the state, we will lose control of New Caledonia in the coming hours.”

Local authorities imposed a curfew, canceled international flights and mobilized 1,700 law enforcement officers. France has since deployed the army and is flying in 1,000 more police officers. The French government has declared a state of emergency, put 10 protest leaders under house arrest, and banned the social media app TikTok in the territory.

Rioters have killed one police officer and fired on several others, according to the French authorities. Another officer was killed by accidental gunfire. At least 64 officers have been injured.

The authorities have said calm has returned to Noumea, but some residents say they are still scared to go out.

“It’s too dangerous,” Fabrice Valette, who lives in the small town of Paita, to the north of Noumea, with his partner and 1-year-old son, said on Friday. “We really don’t know how to get food or drinks or medicine.”

Many protesters appear to be teenagers and young adults who have concealed their identities with masks, three residents said in interviews. At roadblocks and on streets, many protesters are flying the multicolored flag of Kanaky — as New Caledonia is known in the Indigenous language — amid clouds of smoke from burned-out cars and buildings.

The organizer of the protests is a group called the Field Action Coordination Cell, whose leaders said that they did not condone violence. Dominique Fochi, a Paris-based leader of the group, warned that a French crackdown could backfire.

“We hope that sending additional resources there does not offer means of repression, which would only make things worse,” he said,

The constitutional amendment must now be approved by a joint session in the French Parliament, which is scheduled for June.

On Friday, Roch Wamytan, president of the New Caledonian legislature, dismissed requests by Mr. Macron for talks. He said, “How can you discuss with the president of the French Republic in these conditions?”

Nicolas Metzdorf, who represents New Caledonia in the French National assembly, blamed pro-independence leaders for the unrest. He acknowledged there was a risk of a return to civil war.

Gerard Darmanin, the French interior minister, said on Thursday that foreign interference from Azerbaijan had played a role in the unrest. (Relations between the two countries have been strained by France’s support of Armenia in its territorial dispute with Azerbaijan.)

Mr. Darmanin did not provide specifics, and Azerbaijan has denied the allegation.

Some were worried about the escalation of violence in a country where there are a lot of firearms — about one for every four residents.

“Everyone owns guns, so it can get worse very quickly,” said Mr. Valette, the Paita resident. “I think it will be very hard to unite people and be one country after this.”

Reporting for this story was supported in part by the Pulitzer Center.