CALAIS, France — Charles Dufeutrelle used to donate medicine and clothes to the occasional migrant from Afghanistan who came in for coffee at La Gauloise, the bar he owns in Calais, the port city in northern France that has long been a gateway to Britain.
But after a migrant broke into the bar in 2012, Mr. Dufeutrelle, 31, bought aTaser and pepper spray, which he keeps in a drawer near the cash register. And when a group of migrants refused to leave the bar when he asked them to, he pulled out his hunting rifle to scare them away.
That time, the rifle was not loaded, Mr. Dufeutrelle said — but “next time, I will not hesitate to shoot.”
His frustration reflects the resentment and fear that have swept Calais in the last year, along with a new wave of migrants hoping to cross illegally to Britain, which they see as a better place than France to start a new life. The migrants began squatting in vacant buildings and took over shelters in the city center, angering residents and drawing warnings from the local authorities that they could lose control of portions of the city.
Many people here fear devastating repercussions for Calais, which is already suffering from 16 percent unemployment, one of the highest rates in France. Anti-migrant sentiment here has buoyed far-right groups like the National Front party, whose support surged in elections for the European Parliament this past spring.
The National Front’s leader, Marine Le Pen, visited Calais on Friday to denounce what she called the “scandalous carelessness” of the government in a city where “there is nothing left but survival of the fittest, violence.”
Her visit followed unrest in the city on Wednesday, when fights broke out between rival ethnic groups among the migrants and some tried to force their way onto Britain-bound trucks, prompting riot police to step in. Last month, four young Calais residents threw improvised firebombs at a building occupied by Egyptian migrants in the city center.
“The discontent has turned into a real psychosis,” said Emmanuel Agius, the deputy mayor of Calais and a member of the conservative Union for a Popular Movement party. “The migrants of today no longer fear breaking the laws.”
Tensions started to build in Calais more than a decade ago, in 2002, when a Red Cross center in nearby Sangatte was closed down and migrants started to camp around the port instead. The police have dismantled some camps, but the migrants have rebuilt them in new locations.
The local authorities estimate that there are 2,200 to 2,300 migrants around the city now, mostly men who have fled from Afghanistan, Egypt, Eritrea,Ethiopia, Sudan or, most recently, Syria. They wait along the highway leading to the waterfront, hoping to hide in a ferry-bound truck and sneak into Britain. Many of them speak some English and believe they can assimilate better there than in France, even though the British government is adamant about not accepting them.
Britain has called on France to do more to stop the migrants, but “we can’t control them anymore,” said Gilles Debove, a local police officer and a member of the main police union.
About 100 migrants forced their way into Calais’s port last month by tearing down barbed-wire fences. After violence flared this week, the French interior minister, Bernard Cazeneuve, said 100 more police officers would be sent to Calais.
Mr. Debove said migrants in the city took over vacant buildings, stole money and cellphones from residents, fought among themselves and sometimes sexually assaulted local women. He said 80 crimes had been reported in the city this summer involving migrants, up from six a year ago.
In July, hundreds of migrants supported by No Border, an advocacy group, occupied a former metal factory less than a mile from City Hall. At least 100 Sudanese and Eritrean migrants filled the factory one recent day, sleeping on cardboard mats, burning discarded tennis shoes for heat and tapping old water pipes to wash their faces. The floor was littered with empty potato-chip bags and puddles of rainwater from a broken skylight.
“I tried more than 10 times to get inside a truck, but you can die,” said Hassan Abdallah, 30, who said he had fled the Darfur region of Sudan several months ago and crossed the Mediterranean in a fishing boat. “There are no other solutions for us,” he said. “The conditions in which we live force us to do that. You hide, and you think about God.”
Many residents say the situation has left them feeling stressed. Some women say they avoid walking alone in Calais at night. Bar owners say they lost business from local residents after migrants began coming in to charge their phones and use the restrooms.
Sylvie Cambie, who owns a bar called Aux Deux Moineaux, said her sales had fallen by half since Sudanese migrants moved into a shelter nearby. “When my customers see them, they walk away,” Mrs. Cambie said. “I don’t want them, I can’t stand them, and that has nothing to do with racism.”
Philippe Langlois, a guard at the city’s main cemetery, said he had gone into a rage last year when migrants occupied a small plot of land he had bought years ago. “I burned their blankets and made them leave,” Mr. Langlois said. He also padlocked the cemetery restrooms after he saw groups of migrants from a nearby camp using them.
Calais had plenty of problems before the migrants came. A mainstay industry, lacemaking, is in decline, and the city’s biggest employer, the SeaFrance ferry line, went into liquidation in 2012. Though the city is still one of the busiest ports in Europe, traffic has been diminishing, and officials say it could fall further if the migrant problem is not solved.
The situation has also angered many truck drivers, who can be fined $3,200 if they are found to have carried an illegal migrant into Britain, even unwittingly. Last month, some of them threatened to stop delivering goods to England unless the French authorities find a solution.
“If we continue on this path, the city will experience ruin,” said Mr. Agius, the deputy mayor.
The mayor has offered to turn an old community center into a shelter that would house more than 1,000 migrants, and France and Britain have announced plans to strengthen security at the port. But Mr. Dufeutrelle, the bar owner, said he did not think these steps would solve the real problem.
“We need to tell these poor souls that England is no longer an El Dorado,” he said.