A tropical cyclone has hit the island of Madagascar, with winds of up to 194km/h (120mph) ripping up trees and electricity pylons.
At least two people have been killed by Cyclone Giovanna, and there are reports of up to five deaths.
Head of the charity Care told the BBC that 60% of homes in one eastern town had either been damaged or destroyed.
Meteorologists warn the damage may be as bad as in 1994, when a cyclone killed 200 people and displaced 40,000.
Cyclone Giovanna made landfall overnight 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.
Emergency service vehicles have been out in Antananarivo on Tuesday clearing up the debris.
People are staying at home as offices, schools and businesses have been shut and the power has been cut in many areas.
He says he has been unable to ask residents along the eastern coast about the extent of the damage because telephone lines have been brought down by the cyclone.
He warns it could be serious - given that many coastal villagers live in simple houses built of wood and leaves.
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.
Care says it will begin helicopter flights on Wednesday to further assess the damage in the wider Vatomandry district and see where help for those left without shelter or food is most needed.
He said at least five people were thought to have died in the area but that number was likely to increase as more information emerged about the impact of Cyclone Giovanna.
Two people have been killed in the inland sugar-producing town of Brickaville, a government official told the Reuters news agency.
Storm surge warning
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.
Cyclone Giovanna is expected to weaken as it moves across the island, which produces vanilla, coffee and nickel.
But Mr Piggot warned there was still the danger that more lives could be lost and property destroyed.
Coastal towns are at risk of storm surges, where ocean water is pushed ashore, in this case of between 2m and 3m (7f and 10ft), he said.
The whole island could also see rainfall of between 10in and 20in (25cm and 50cm), which could lead to dangerous landslides.
The storm will head next towards southern Mozambique, he said.