Tropical storm Ana has killed at least 34 people in Madagascar and three people in Mozambique, while knocking out power in Malawi, authorities in the three countries said Tuesday.
The storm, which formed over the east coast of Africa's largest island Madagascar, has brought heavy rains causing flooding and mudslides in the capital Antananarivo.
The latest report from Madagascar's disaster management agency on Tuesday showed that 34 people have died and nearly 65,000 have been left homeless since last week.
Several low-lying districts of the capital remain under high alert and emergency evacuations were launched overnight.
"We are in the process of evacuating people from flooded areas," John Razafimandimby, rescue unit director in the disaster management agency, told AFP.
Across the Indian Ocean, the storm made landfall on mainland Africa on Monday bringing heavy rains and strong winds in Mozambique's central and northern districts.
Mozambican officials on Tuesday said three people were killed, with at least 66 others injured.
More than 3,800 people have so far been affected while a clinic and 16 school classrooms were destroyed overnight, according to the National Institute for Disaster Risk Management.
The UN forecasts the storm will cause widespread flooding, uproot people and damage infrastructure.
The storm will potentially affect "highly vulnerable populations who have already suffered from previous natural disasters and conflict in northern Mozambique," the UN Office for the Coordination of Humanitarian Affairs said in an update.
Government and UN agencies estimate that 500,000 people may be impacted in Mozambique's Nampula, Zambezia and Sofala provinces.
In neighbouring Malawi, the storm plunged most parts of the country into darkness overnight Monday after flash floods raised the water levels, forcing the electric company to shut down its generators.
"Our generation depends on water levels, and currently the levels are too high for us to run the machines. It is too risky," Moses Gwaza, spokesman for the power utility Electricity Generation Company, told AFP.
In an update on Tuesday morning, the company said it was starting to restore power generation.