Aid agencies have described the damage caused by Cyclone Idai in southeast Africa as 'staggering'.
The powerful storm hit Mozambique, Zimbabwe and Malawi around a week ago, bringing winds of around 195 km/h at times.
It led to serious flooding as rivers burst their banks - blocking off large areas and cutting communication lines.
Associated Press reports that the death toll in the three countries has now climbed past 600.
However, that number is expected to rise.
Elhadj As Sy, secretary general of the International Federation of Red Cross and Red Crescent Societies (IFRC), visited Beira in Mozambique.
The port city is one of the worst affected areas, with aid workers on the ground saying around 90% of the area around it was destroyed.
Mr Sy said: "The scale and scope of suffering and damage is breath taking. Hundreds of thousands of people have been impacted in some way. We must respond fast and at scale, and prepare to accompany the affected populations on a longer term.
"I was able to fly over some of the flooded areas. The scale of this crisis is staggering."
He added: "But we can’t forget that it is an intimate and human crisis. Tens of thousands of families have lost everything."
The charity warns that there's growing disease among aid workers about possible disease outbreaks - noting there's already been some cholera cases reported in Beira.
They also said there's been an "increasing number of malaria infections among people trapped by the flooding".
Meanwhile, aid workers are continuing their operations in the region - attempting to reach areas that have been worst hit.
Some of our most experienced emergency responders are on the way to flood-affected areas.
The rains continue and flood levels are rising in many places, making it difficult for teams and emergency supplies to reach people in need. pic.twitter.com/UzJVHuMjnh
— Doctors w/o Borders (@MSF_USA) March 21, 2019