Cyclone Idai lashed the Mozambican port city of Beira with winds of up to 170 km per hour (105 miles per hour) last week, then moved inland to Zimbabwe and Malawi, swamping populations and devastating homes.
"Hundreds of people have been killed and hundreds of thousands more have been affected by what the United Nations says could be "one of the worst weather-related disasters ever to hit the southern hemisphere", its report stated. This is the highest death toll for all three countries which were devasted by the cyclone. Aid workers say that number is certain to rise as flood waters recede.
"The awful magnitude of the disaster that the sheer brutal force of Cyclone Idai caused, and the devastation that it left in its wake, caused the United Nations to declare that it is the worst natural disaster to have ever hit the Southern Hemisphere", he said.
"We're going to have to wait until the flood waters recede until we know the full expanse of the toll on the people of Mozambique", OCHA coordinator Sebastian Rhodes Stampa said.
A satellite image shows an aerial view of Beira city, Mozambique, before the cyclone.
Thousands remain trapped by the floodwaters, and numerous Mozambican government's relief centres have only just started receiving food supplies. The International Federation of Red Cross and Red Crescent Societies (IFRC) warned of the risk of other outbreaks, already noting an increase in malaria.
As part of its relief operations in cyclone-hit Mozambique, the Indian Navy has rescued more than 192 people and provided assistance to 1,381 people in medical camps set up by it, a statement said.
Aid groups said Mozambique had borne the brunt of flooding from rivers that flow downstream from neighbouring countries. "Television footage and photos of entirely families, women, and children trapped on roof tops or holding onto tree branches for dear life with torrents of storm water mere metres beneath them have deeply touched the hearts of South Africans", Magashule said.
"We are living an unprecedented natural disaster".