Cyclone Chido hit the far north of Mayotte at around 15:00 local time (12:00 GMT) on Saturday as an intense tropical cyclone, equivalent to a major category four hurricane.
Wind speeds of 226 km/h (140 mph) were recorded as the cyclone made landfall on the island.
Wave heights were also estimated to be between four and eight metres (13-28ft) on the north coast of the island.
It is the strongest cyclone to have hit Mayotte in 90 years.
After clearing away from Mayotte, Cyclone Chido continued its path westwards, and made its third landfall on Sunday just south of Pemba in Mozambique at 08:00 local time (06:00 GMT).
Although it had weakened slightly, it was still a major cyclone, with a well-defined eye, and winds above 200km/h (124 mph).
The storm then continued to advance inland through Mozambique and Malawi.
As it now moves over land, the winds are weakening rapidly, and the storm has been on downgraded to a “depression”.
The winds are around 48km/h (30 mph), but the main threat is now the rainfall.
Intense downpours are expected to lead to flooding and landslides as the system moves in a south-west direction.
During Monday, it will cross southern Malawi, then Mozambique’s Tete province, before heading towards Zimbabwe overnight into Tuesday.
In the path of the storm, there could be 150-300mm of rain by the end of Tuesday.
The situation on Mayotte is “chaotic”, according to Eric Sam Vah from the French Red Cross.
He’s based on the French island of Réunion – on the opposite side of Madagascar to Mayotte – and has been speaking to BBC Radio 4’s Today programme.
He says he’s been receiving reports from French Red Cross volunteers on Mayotte. They have around 200 people on the ground there, he says, but they have only been able to reach around 20 of them.
Most of their volunteers, he says, have been “personally affected”.
“We still have limited information because of the difficulty of communication,” Sam Vah says, adding the French authorities sent the first aid to the island over the weekend and more support is expected.
Around 100,000 on the island live in slums, he says.
“Most of the slums have been totally destroyed. And we haven’t received any report of displaced people. So the reality could be terrible in the coming days,” he says.
Recuse operation a struggle after devastating cyclone.
It’s a struggle for the rescue teams in Mayotte who have begun the search for possible survivors following the devastating cyclone over the weekend.
So far, France has deployed 110 soldiers, with an additional 160 expected to arrive later today when the French interior minister visits.
But it’s difficult because the search operation has been hampered by damage to the infrastructure across the island.
Moving around is also hard as the roads have been damaged, the power lines are down, and communication has been cut.
It’s a very desperate situation.
Mayotte is a French island in the Indian Ocean.
It lies in the north of the Mozambique channel off the coast of south east Africa, between Madagascar and Mozambique.
Mayotte is made up of two main islands: Grande-Terre and Petite-Terre. The nearby Comoros cover three small volcanic islands. Unlike Mayotte, Comoros declared independence from France in 1975.
Mayotte has a population of 321,000 people. Earlier this year, many migrants arrive every week, many from Comoros.
