About 1.85 million people have now been affected by Cyclone Idai and its aftermath in Mozambique alone, a UN humanitarian agency says.
Idai flattened homes and provoked widespread flooding when it made landfall near the Mozambique port city of Beira on March 14, before ripping through neighbouring Zimbabwe and Malawi.
As of Tuesday, at least 686 people had been reported killed by the storm, the flooding it caused and heavy rains before it hit.
Aid workers are racing to fathom the scale of the disaster and determine what help is most urgently needed, the UN Office for the Coordination of Humanitarian Affairs (OCHA) said on Tuesday.
"Some will be in critical, life threatening situations. Some will sadly have lost their livelihoods, which whilst an appalling tragedy is not immediately life threatening," OCHA coordinator Sebastian Rhodes Stampa said.
At least 686 people have been killed by the storm and its aftermath across the three countries, a figure that could rise as relief workers prepare for what they say are inevitable outbreaks of diseases including malaria and cholera.
Mozambique remains the hardest hit by the humanitarian crisis with tens of thousands of homes destroyed and hundreds of thousands displaced across an area of some 3000 square kilometres.