Chido spared the Comoros but devastated the French territory of Mayotte just 70 kilometres (43 miles) away, an Indian Ocean magnet for migrants from impoverished Comoros islands and elsewhere in search of a better life.

Faiza Soulaimana, 31, told AFP she had not heard from her aunt in Mayotte since the storm struck on Sunday, wiping out shantytowns, largely severing communications with the islands and leaving a death toll that authorities fear will reach into the hundreds.

"Since the cyclone, no one has been able to reach her. I am very worried because she is diabetic and is on dialysis," Soulaimana, a nurse, said by telephone from the town of Domoni, from where it is possible to see the French territory on a clear day.

Her aunt had gone to Mayotte two years ago for medical treatment and ended up staying, also bringing over her two children, she said.

Migrants are estimated to make up nearly half of Mayotte's population of around 320,000 people, according to the latest French statistics from 2017. Among them, 95 percent were Comoran.

Many of them live in Mayotte's numerous shantytowns.

"Andhum, my big brother, has been living in Mayotte for less than a year. I don't know if he is dead, I don't know if he is injured," said a man from the Grande-Comore, the largest of the Comoros's three islands.

"Since the cyclone, no one in my village has been able to get news of relatives who have settled in Mayotte," he told AFP, asking to remain anonymous for fear of causing trouble for his brother, an undocumented migrant.

- 'No news' -

The Comoros on Monday declared a week of national mourning after Chido devastated the territory.

Oussein Mahmoud, 48, told AFP that he was worried about his best friend, Janot, who had moved to Mayotte's Petite-Terre island.

"I have not been able to have any news of him. My wife has no news of her family there either," he told AFP.

A collective called "Solidarité Chido" has been formed to raise money for Comorans in Mayotte affected by the disaster, said Sitti Djaouharia Chihabiddine, one of the organisers.

She too has had no news of several relatives, whether those "living in solid houses, like my brother, who lives in Petite-Terre, or a relative who lives in a shantytown," she said.

A source close to the authorities in Mayotte told AFP on Saturday that an estimated 100,000 to 200,000 people there were irregular migrants.

But few undocumented migrants went to accommodation centres before the cyclone hit, "probably for fear of being checked", the source added. "All the shantytowns are flattened, which suggests a considerable number of victims."