The death toll in Mozambique from Cyclone Idai could reach 1,000, President Filipe Nyusi has said.
It made landfall close to the port city of Beira on Thursday with winds of up to 177 km/h (106 mph), but aid teams only reached the city on Sunday, reports BBC.
The official death toll stands at 84 following flooding and high winds, which have destroyed homes and ripped roofs from concrete buildings.
The cyclone has killed at least 160 people across southern Africa.
On a visit to Beira, President Nyusi said that its impact had been devastating, adding that he had seen bodies floating in the floodwater.
Earlier, the International Federation of Red Cross and Red Crescent Society (IFRC) described it as "massive and horrifying".
People have had to be rescued from trees, said head of the IFRC assessment team, Jamie LeSeur.
In neighbouring Zimbabwe, more than 80 people have died in the east and south, information ministry head Nick Mangwana told Reuters news agency.
This includes two pupils from the St Charles Lwanga boarding school in the district of Chimanimani, who died after their dormitory was hit when rocks swept down a mountain.
Malawi has also been badly hit. The flooding there, caused by the rains before the cyclone made landfall, led to at least 122 deaths, Reliefweb reports.