Authorities in Tanzania have advised people in southern coastal regions to move to safer ground ahead of the expected arrival of a cyclone.
Cyclone Kenneth is predicted to also hit neighbouring northern Mozambique with winds of up to 200km/h (124 mph) and torrential rain.
Residents have been told to expect damage to their houses and farms.
Mozambique is still reeling from Cyclone Idai which killed hundreds of people and left thousands homeless.
The storm made landfall near the port city of Beira on 14 March, packing winds of up to 177 km/h and bringing torrential rain which caused extensive flooding.
More than 700 people were killed in Mozambique, Malawi and Zimbabwe and at least three million were left in need of humanitarian assistance.
Tanzania's Lindi, Mtwara and Ruvuma regions have been listed as the most prone to the weather, which is predicted to hit the country on Thursday.
Authorities have urged people who live in mud houses to seek shelter where they would be safe.
The storm is forecast to also affect Mozambique's northern Cabo Delgado province.
In the island nation of Comoros will also feel the impact. Authorities there have closed airports for at least 24 hours as a precautionary measure against the cyclone expected there on Wednesday, reports privately-owned Comores Infos news website.
Schools have also been closed, it adds.
Cyclone Kenneth could be the strongest cyclone ever recorded to make landfall in southern Africa, BBC Weather reports.