Emergency workers and families on Monday desperately searched for victims after a storm devastated the French territory of Mayotte, off the eastern coast of Africa. Officials fear that hundreds or even thousands could be dead, far higher than the current confirmed toll of 21.

Tropical Storm Chido, which hit over the weekend, destroyed homes, schools and businesses on the tiny archipelago, with wind gusts of up to 124 miles per hour. Forecasters said that it was the worst storm in 90 years to hit the territory.

Mohamed Abdallah, the father of a family of seven, said that they had “lost everything.” As he picked up pieces of iron on the streets to rebuild a shelter on Monday, he said, “It will take us a while to even be safe.”

France’s president, Emmanuel Macron, led an emergency meeting in Paris on Monday evening to coordinate the government’s response. He said afterward that he would soon go to Mayotte and declare a period of national mourning.

France is sending over 1,200 firefighters, security forces and rescue workers, and has started aid flights carrying tons of tents, beds, food and water from Réunion, another French territory in the region.

The interior ministry said that 21 people had died in the hospital, and that over 1,300 people had been injured. However, François-Xavier Bieuville, France’s top-ranking representative on Mayotte, told a local news channel, “I think that there will be several hundred” deaths.

“Maybe we will be closer to a thousand, maybe several thousand,” he added.

The interior ministry cautioned that officials would likely be unable to count all the victims. About a third of the territory’s 320,000 people are undocumented immigrants, many of them living in precarious housing, the ministry said, which could complicate official tallies. Also, many residents are Muslims, who traditionally try to bury their dead within 24 hours.

In Pamanzi, home to Mayotte’s airport and many administrative buildings, the buzz of chain saws filled the air on Monday as emergency workers scrambled to clear uprooted trees and debris. Doctors worked in flooded health care centers. Children slept on mattresses outside of houses that had been torn apart.

“There are people who haven’t had anything to eat or drink since yesterday,” Salama Ramia, a French senator who represents Mayotte, told French television outlet BFMTV on Monday from the archipelago.

Water use on the archipelago had already been restricted in recent weeks because of drought. Last year, Mayotte experienced its worst drought in over two decades, which had led to protests over accusations of mismanagement and cuts to service.

Ms. Ramia said emergency workers had not yet been able to reach some neighborhoods that had been demolished, adding to uncertainty about the death toll.

“We are worried about what we will find,” she said.

But Mayotte, France’s poorest territory, was already struggling before the storm hit on Saturday. The health care system was “on its last legs,” according to a 2022 French Senate report, with a single overburdened hospital and a severe shortage of doctors.

About 80 percent of the population lives below the poverty line, five times more than the percentage in the rest of France. Many people on Mayotte are crowded into shanty towns, which were hit especially hard. Videos and photos showed the destruction: Homes were destroyed, debris was strewn about hillsides and trees had been ripped apart by wind.

“Some shanty towns were completely devastated,” Ambdilwahedou Soumaila, the mayor of Mamoudzou, the capital of Mayotte, told French television on Sunday.

Mayotte has recently become a focal point for bitter French debates around immigration. The population has grown rapidly, which has strained social services. And French security officials have intervened in recent years to try to crack down on illegal immigration and unsanitary housing.

Much of the increase comes from an influx of undocumented immigrants, many from Comoros, a neighboring archipelago that is one of the world’s poorest countries.

In February, the French interior minister tried to make Mayotte less attractive to immigrants by pushing to end birthright citizenship there. The effort, which some argued was a serious breach of French values that would do little to deter migrants, came to a halt when Mr. Macron called snap elections this summer.

Bruno Retailleau, France’s departing interior minister, dismissed suggestions that the authorities were ill-prepared for the storm, arguing instead that the devastating impact was largely because thousands of undocumented immigrants live in shoddy housing.

“That’s the weak point,” he said. “But the alert and forecasting systems worked perfectly.”

Mozambique also suffered serious damage, although the death toll there appears lower: Chido killed at least three people, according to an early estimate, local officials told the French news agency Agence France-Presse.

The storm, which has since been downgraded to a depression, is expected to dissipate by Tuesday.

Guy Taylor, the spokesman in Mozambique for the United Nations Children’s Fund, said that aid teams were traveling to rural areas throughout the northern part of the country on Monday to assess the situation.

The organization fears that many of those communities, which already had little access to clean water and sanitation, would be susceptible to cholera outbreaks.

On Monday, families in Mayotte were still trying to reach relatives, even though mobile and internet networks were disrupted. Outages kept Mayotte almost entirely offline for more than 36 hours, according to NetBlocks, an internet monitoring group.

Many people posted desperate pleas on a Facebook page to try to find loved ones. Some ended their posts with a statement of solidarity: “Force à tous,” or stay strong.