The former Portuguese colony, suffering from nearly two weeks of persistent rains, has already made an appeal for $2.7 million in immediate aid.
Donors, including the former colony power, the United States and European states have already pledged $2 million. Neighbouring South Africa has provided military helicopters to help in the rescue effort.
The United Nations Children's Fund has committed $400,000 in emergency funds to support relief efforts by the government and various relief agencies.
"The latest estimate is that 300,000 people are affected and need emergency food aid for at least the next three months," said Silvano Langa, director of the National Disasters Management Institute, told reporters.
The World Food Programme in Maputo has moved to import 5,000 tonnes of emergency basic foodstuffs.
One press report has estimated the death toll at 48 with a further 15 missing. Though there is no official statement on the number of deaths, fatalities were expected to rise.
The country also faces a potential outbreak of cholera and malaria in flood-ravaged areas.
"Our chief concern right now is the threat of disease. There is a serious sanitation problem, which is increasing the risk of cholera outbreaks," said UNICEF official Mark Stirling.
Gaza and Maputo provinces have been the most badly damaged regions and were braced for further flooding as the Limpopo River burst it banks.
The flood was expected to hit Xai-Xai city, home to more than 100,000 people, in Gaza province later on Wednesday. The province's second largest city, Chokwe, is already under water, threatening the region's crops.
The Gaza Flood Commission warned that anyone still in low-lying parts of Xai-Xai should move to higher ground.
An estimated 27,000 people have been cut off in the province as rivers reached record highs. Roads to Swaziland and South Africa have been overrun by flood waters.
South African weather experts predicted no end to the rain in the region.
"It's going to get a lot worse for the next day and a half before its gets better," said Tali Freiman, a researcher at the climatology unit at Wits University in Johannesburg.
At least 50 people have died in South Africa in the country's worst flooding in more than five decades. Parts of the Northern Province and Mpumalanga have been declared disaster zones after rainfall levels hit as much as 600 mm in 24 hours.
- Reuters - Thomson Reuters Foundation
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