At least 10 people have been killed by Cyclone Giovanna, officials in Madagascar have said.
There are reports of up to six more deaths - with more expected as emergency workers try to establish the extent of the destruction.
The tropical cyclone hit the Indian Ocean island on Tuesday, with winds of up to 194km/h (120mph).
Meteorologists warn the damage may be as bad as in 1994, when a cyclone killed 200 people and displaced 40,000.
Richard Ramandeamanana, a government official in Alaotra Mangoro, told the AP news agency on Wednesday that seven people in his eastern region were killed when Cyclone Giovanna struck land early on Tuesday.
His toll included six killed when a building collapsed.
Three deaths had been reported in other regions, including two in the badly-hit inland sugar-producing town of Brickaville - and on Tuesday the charity Care says it received reports of five deaths elsewhere.
The worst of the storm was over by Tuesday afternoon - but large parts of the country have been cut off by the storm, making it difficult to fully assess how much damage has been done to agriculture, livestock and homes.
Food relief agencies have been using helicopters to fly over the island and see what has happened - and find out where help for those left without shelter or food is most needed.
But they say it is still too early to pinpoint exact numbers of people affected by the cyclone, which brought heavy rain and high winds, ripping up trees and electricity pylons.
Cyclone Giovanna made landfall near the eastern port city of Toamasina, also known locally as Tamatave, 200km (about 125 miles) from the capital, Antananarivo.
Antananarivo-based journalist Tim Healy told the BBC's Network Africa programme that the capital city experienced very high winds and heavy rainfall for most of the day on Tuesday.
There are reports of mudslides along the main Toamasina-Antananarivo road.
Toamasina, Madagascar's main port, has not been as badly damaged as initially thought, director of the charity Care International John Davis told the BBC.
But preliminary assessments of the smaller town of Vatomandry - which is home to about 40,000 people and is less than 50km south of where Cyclone Giovanna first hit land - has been badly damaged, he said.
"Our people on the ground in Vatomandry estimate that at least 60% of homes were damaged or destroyed," he said.
"The sturdier houses may have just lost roofs, while traditional structures made of palm leaves and bamboo were often destroyed," he added.
He said at least five people were thought to have died in the wider Vatomandry district but that number was likely to increase as more information emerged about the impact of Cyclone Giovanna.
The government of Madagascar issued the first warnings on Monday afternoon - but residents say the intensity of the cyclone was not explained.
Town criers, who walk around the streets ringing a bell and shouting out information in the local Malagasy language, are normally used by the government in a time of crisis.
But Mr Healy said they were not heard on Monday and it has left many people taken aback by the storm's severity.
Madagascar, the world's fourth largest island, is prone to cyclones and tropical storms, especially in the rainy season between February and May.
Mike Piggot, a meteorologist with the US-based monitoring body AccuWeather, told the BBC the storm was of a similar strength to Cyclone Geralda.
It was one of the worst cyclones to hit Madagascar, in the Indian Ocean, and destroyed about 300,000 hectares of crops and left thousands homeless in 1994.
The storm is heading towards southern Mozambique.