The island’s governor, François-Xavier Vieuxville, told local media the death toll could rise significantly once the damage is fully assessed. He warned that the number was “definitely in the hundreds” and could be in the thousands.
Mayotte’s impoverished communities, including undocumented migrants who have traveled to French territory to seek asylum, are thought to have been particularly hard hit by the vulnerable nature of their housing.
The Islamic tradition of burying the dead within 24 hours makes recording the death toll more difficult, the governor said.
In addition to the relief effort, 110 French troops have arrived to assist with the rescue, with 160 more expected to arrive.
After arriving in Mayotte, French Interior Minister Bruno Retailleau said it would take “a few days” to confirm any casualties.
Relief efforts are being organized in Réunion, another French overseas territory.
French Red Cross spokesman Eric Sam Vah told the BBC the situation was “confusing”.
He expressed concern about the overall death toll, saying he had been able to contact only 20 of Mayotte’s 200 Red Cross volunteers.
“The whole slum has been completely destroyed,” Mr Barr told BBC Radio 4’s Today programme. “We have not yet received any reports of displacement.”
France colonized Mayotte in 1841, and in the early 20th century added the three major islands that make up the Comoros archipelago to its overseas territories.
The Comoros chose independence in 1974, but Mayotte decided to remain part of France.
The island’s population is heavily dependent on French financial support and has long suffered from poverty, unemployment and political instability.
About 75% of the population lives below the national poverty line, and unemployment is around one in three.
