Parts of the islands, which were struck by Cyclone Chido over the weekend with winds of more than 200km/h. remain inaccessible to rescue workers, Reuters reports.
The storm was the strongest to strike Mayotte in more than 90 years, French weather service Météo France said. It has a population of about 321,000 and is made up of two main islands over an area about twice the size of Washington DC.
Rapid intensification of cyclones is also more likely with higher sea temperatures and so the fact that this storm strengthened so quickly may have been partly due to climate change, BBC reports.