Rapidly rising floodwaters have created "an inland ocean" in Mozambique endangering thousands as aid organisations scramble to rescue and feed survivors of Cyclone Idai.
Mozambique's swollen rivers have already flooded huge expanses of the country and continued rains are causing the waters to rise.
World Food Program (WFP) spokesman Herve Verhoosel said the situation was a major humanitarian emergency that was getting bigger by the hour.
He said large numbers of people are "crammed on rooftops and elevated patches of land outside the port city of Beira" and WFP is rescuing as many as possible while providing airdrops of food, water and blankets.
Mozambique's Pungue and Buzi rivers have overflowed, creating "inland oceans extending for miles and miles in all directions", Verhoosel said.
Cyclone Idai created massive damage as it swept across central Mozambique before dropping huge amounts of rain in Zimbabwe's eastern mountains.
That rainfall is now rushing back through Mozambique further inundating the already flooded countryside.
The flooding disaster is also affecting Malawi and Zimbabwe where hundreds are dead, many more are missing and thousands are at risk.
Mozambique's President Filipe Nyusi has said the death toll could reach as high as 1000.
Australian Associated Press