Doctors in the Haitian capital, Port-au-Prince, say a deadly outbreak of cholera has reached the city.
There are fears that the outbreak, which the Health Ministry says has killed 544 people, could spread quickly through camps in the capital where hundreds of thousands of survivors of January's earthquake are living.
An aid organisation has told the BBC that it is treating at least 30 suspected cholera cases in the city.
When visiting the city's biggest slum, Cite Soleil, the BBC's correspondent was told by two patients suffering from severe vomiting and diarrhoea that people had died from cholera in their neighbourhoods.
Authorities fear the outbreak could worsen as a result of the heavy rains brought last week by Hurricane Tomas, which itself claimed at least 20 lives.
Fear that flooding could spread disease
Susan Barry, from the charity Christian Aid, says people in the Leogane area are using brooms and shovels to remove the worst of the thick mud left by the hurricane.
She says the main concern is that the flooding could spread the cholera, with people having no alternative but to drink contaminated water, while lacking access to basic sanitation.
Cholera causes diarrhoea and vomiting, which can lead to severe dehydration. It can kill quickly but is easily treated through rehydration and antibiotics.
On Friday, Haiti's government and the United Nations appealed to donors for $24 million to cover urgent humanitarian needs.