Mozambique's cyclone-hit city of Beira has confirmed its first death from cholera, as the number of cases of the disease has jumped to 517.
To control the outbreak, emergency clinics have been set up across Beira, a city of 500,000, said Mozambican national health director Ussene Isse, according to broadcaster TVM.
Cases of the acute disease have risen dramatically since the first five cases were confirmed last week.
Cyclone Idai severely damaged the water system for Beira when it hit on March 14.
Some 900,000 cholera vaccine doses were set to arrive on Monday, according to the World Health Organisation.
Cholera is spread by contaminated water and food.
It can kill within hours but is relatively easy to treat.
The overall cyclone death toll in Mozambique is now 518.
With 259 deaths in Zimbabwe and 56 in Malawi, the three-nation death toll is more than 815.
Authorities warn the tolls are preliminary as flood waters recede and reveal more bodies.
The Chinese government has sent doctors and emergency workers to fight the cholera outbreak in Beira and Chinese aid workers sprayed anti-cholera disinfectant in parts of the port city.
The US military joined the international humanitarian aid efforts to Mozambique by airlifting food and relief supplies from South Africa.
Beira's crowded, poor neighbourhoods are especially at risk.
Doctors Without Borders has said it is seeing some 200 likely cholera cases per day in the city, where relief workers are hurrying to restore the damaged water system and bring in additional medical assistance.
Cholera is a major concern for the hundreds of thousands of cyclone survivors in the southern African nation now living in squalid conditions in camps, schools or damaged homes.
Some drink from contaminated wells or filthy, stagnant water.
As health personnel stress the need for better disease surveillance, the United Nations' deputy humanitarian coordinator in Mozambique, Sebastian Rhodes Stampa, has said all cases of diarrhoea are being treated as though they are cholera.
Cholera is endemic to the region, and "it breaks out fast and it travels extremely fast", he told reporters.
Doctors Without Borders has said other suspected cholera cases have been reported outside Beira in the badly hit areas of Buzi, Tica and Nhamathanda but the chance of spread in rural areas is smaller because people are more dispersed.
Australian Associated Press