(CNN) -- Torrential rains sent rivers raging through towns in Mozambique, ripping up homes and killing at least 36 people over the past few days.
Tens of thousands fleeing affected areas remain stranded without food and water as fears of a humanitarian crisis grow.
"Intense rains and flooding of the Limpopo River have affected over 100,000 people in Gaza Province alone," the United Nations said in a statement.
Evacuees waded through flowing muddy waters, a few prized possessions perched on their heads. Others scrambled to climb atop roofs to avoid drowning.
"In Chokwe, one of the hardest hit districts -- the normally vibrant streets now lie under water --all business brought to a standstill and social services shut down," the United Nations said.
Preliminary information indicates at least $15 million will be needed for the relief operation. The United Nations warned that the amount is expected to go up as assessment teams release more information.
In 2000, the southern African nation suffered devastating floods that killed at least 700 people and displaced millions.
The floods more than a decade ago destroyed highways and bridges, and prompted fears that land mines left over from a civil war may have shifted.