''We're expecting heavy storms over the weekend. They will hit the most vulnerable areas,'' said Ian MacLeod, emergency coordinator for UNICEF.
There was no official estimate of the death toll as of Friday, although local media reports said it was at least 48.
Heavy rains have also dislodged landmines, a legacy of the African country's 16-year civil war that ended in 1992.
''There's no doubt that landmines are in the Limpopo Valley and they will have been exposed by the rains,'' MacLeod said.
He said that 220,000 people had been displaced or lost their homes in the worst-hit provinces, Maputo and Gaza, after the worst flooding in memory hit Mozambique, a former Portuguese colony located in southeastern Africa.
Some 150,000 people who had gathered in 20 locations on high ground in the Limpopo Valley to escape rising flood waters needed urgent food, clean water and shelter, MacLeod said.
A total of 800,000 people were vulnerable to malaria, cholera, other water-borne diseases.
Gaza and Maputo provinces have been the most badly damaged regions and were braced for further flooding as the Limpopo River, which takes rain from South Africa, Botswana and Zimbabwe into Mozambique, burst its banks.
The United Nations was preparing to launch an inter-agency appeal on Monday, according to Katarina Toll Velasquez, head of the U.N. Disaster Assessment and Coordination (UNDAC) team.
''An appeal will be made on Monday...There is intense contingency planning under way now,'' Velasquez said.
UNDAC estimated that 225,000 people were in need of emergency food aid with a potentially 75,000 more at risk.
UNDAC has already come across cases of malaria at temporary care centres in the capital Maputo.
The Mozambique government has appealed for $2.7 million in immediate aid.
Donors, including Portugal, the United States and European states, have already pledged $2 million. Neighbouring South Africa has provided military helicopters to help the rescue effort.
- Reuters - Thomson Reuters Foundation
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