The cyclone hit the country's second largest city, Toamasina, on Tuesday with wind speeds of up to 70 meters per second.
Trees have been uprooted and many houses have had their roofs torn off. The storm has also triggered widespread flooding.
"It's total chaos," says Rija Randrianarisoa, head of disaster management at the aid organization Action Against Hunger.
"It is impossible to get around on the roads, which are blocked by trees and debris."
Many of the deaths are reported to have been caused by collapsed buildings. Four people are still missing and at least 36 people are seriously injured.
