SAINT-DENIS DE LA REUNION -- France said it will impose a nighttime curfew on the Indian Ocean island of Mayotte from Tuesday evening, after the French overseas territory was devastated by a cyclone feared to have killed hundreds.

According to the latest official toll, 21 people are confirmed to have been killed by Cyclone Chido when it barreled into the island and its surrounding archipelago at the weekend.

But authorities fear that hundreds, and possibly even thousands, will be confirmed killed once the true scale of the toll is revealed after the rubble is cleared and roads are unblocked.

In a sign of the potential magnitude of the tragedy, the Red Cross said it feared more than 200 of its volunteers were missing on Mayotte.

The health services are in tatters, power and mobile phone services have been knocked out, the airport is closed to civilian flights while there is mounting concern about how to ensure supplies of drinking water.

Cyclone Chido is the latest in a string of storms worldwide fueled by climate change, according to experts.

The curfew from 10:00 pm to 4:00 am local time (1900 GMT to 0100 GMT) is being put in place as a security measure to prevent looting, the French interior ministry said.

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- 'Completely devastated' -

French President Emmanuel Macron, who chaired a crisis meeting on Monday night, has described the situation as a "tragedy" and promised to visit Mayotte in the coming days.

Interior Minister Bruno Retailleau, who on Monday visited the island, said that Mayotte has been "completely devastated", with 70 percent of inhabitants affected.

"The toll will be heavy, too heavy," Retailleau warned.

He announced the arrival "in the coming days" of 400 additional gendarmes to reinforce the 1,600 gendarmes and police officers present on the archipelago, while specifying that there had "not really been any looting" so far.

The "exceptional" cyclone was super-charged by particularly warm Indian Ocean waters, meteorologist Francois Gourand of the Meteo France weather service told AFP.

Mayotte is France's poorest region, with an estimated one third of the population living in shantytowns whose flimsy sheet metal-roofed homes offered scant protection against the storm.

"We're starting to run out of water. In the south, there's been no running water for five days," said Antoy Abdallah, a resident of Tsoundzou in the territory's capital Mamoudzou.

"We're completely cut off from the world," the 34-year-old lamented.

Most of Mayotte's population is Muslim and religious tradition dictates that bodies must be buried rapidly, meaning some may never be counted.

And assessing the toll is further complicated by irregular immigration to Mayotte, especially from the Comoros islands to the north, meaning much of the population is not even registered.

Mayotte officially has 320,000 inhabitants but authorities estimate there could be 100,000 to 200,000 more people, taking into account illegal immigration.

Ousseni Balahachi, a former nurse, said some people did not dare venture out to seek assistance, "fearing it would be a trap" designed to remove them from Mayotte.

Many had stayed put "until the last minute" when it proved too late to escape the cyclone, she added.

After hitting Mayotte, Cyclone Chido made landfall in Mozambique, claiming at least 34 lives and destroying 23,600 homes, authorities said.

- 'Not seen for decades' -

Mayotte is one of several French overseas territories which are ruled from Paris.

French military planes have been shuttling between Mayotte and the island of La Reunion, also a French overseas territory, to the east which was spared the cyclone and is serving as the hub for rescue efforts.

The first air evacuation of 25 badly wounded people from Mayotte to La Reunion took place on Monday night, Health Minister Genevieve Darrieussecq said.

The disaster poses a major challenge for a government still only operating in a caretaker capacity, days after Macron appointed the sixth prime minister of his presidency.

New Prime Minister Francois Bayrou was facing a torrent of criticism less than a week into the job after choosing to chair a provincial town hall meeting in his capacity as mayor of Pau instead of attending in person Macron's crisis meeting.

French National Assembly speaker Yael Braun-Pivet, a member of Macron's centrist party said Bayrou needed to be "side-by-side with the people".

"I would have preferred that the prime minister, instead of taking a plane for Pau, took a plane for Mamoudzou," she told Franceinfo radio.

© Agence France-Presse