The death toll from cholera across Haiti has risen to 644, as aid workers fight to contain the spread of the disease in the capital, Port-au-Prince.
At least 10,000 people suffering from cholera are in hospitals across the country.
Doctors in Port-au-Prince say they are alarmed at the speed at which new cases are emerging.
A senior health ministry official said the epidemic was now "a matter of national security".
The ministry on Tuesday confirmed the disease had reached Port-au-Prince, which had feared an outbreak since October.
About 170 people are now being treated in hospitals in the city, according to the Pan-American Health Organisation (Paho). One person has died.
'Cross the border'
Dan Epstein, a Paho spokesman, said the organisation expected 270,000 Haitians to be infected by the disease in "between six months and a year", according to modelling based on a past outbreak in Peru.
"What's really important to us now is the trend of where it is and the long term trend of where it is going to be," he told the BBC.
"Its hard to predict the impact. But it's very likely that cholera is going to be in Haiti for a while," he added.
Paho has warned that there is a real risk of the epidemic crossing the border into the neighbouring Dominican Republic.
The organisation says that trying to educate the population about prevention and treatment of the disease, thereby reducing the fatality rate of the disease in the Caribbean country, remains a priority.
The disease broke out in the Artibonite River valley in central Haiti in mid-October and initially seemed to have been contained, but cases have since soared.
Officials are warning that a sizeable outbreak in Port-au-Prince, where 1.3 million earthquake survivors live in tents, is now likely.
"The epidemic of cholera, a highly contagious disease, is no longer a simple emergency, it's now a matter of national security," the director of Haiti's health ministry, Gabriel Thimote, told a news conference.
Meanwhile, desperate scenes were described in the northern town of Gonaives, in the Artibonite region.
"Sick people died on the way to the hospital, the bodies were covered in blankets and left near the town cemetery," mayor Adolphe Jean-Francois told AFP.
The water-borne disease has already spread to half of Haiti's 10 regions.
Flooding caused by Hurricane Tomas is believed to have exacerbated conditions and helped spread the disease further, officials have said. The storm at the end of last week left 20 people dead, with 36 injured and 11 missing.
Cholera itself causes diarrhoea and vomiting, leading to severe dehydration. It can kill quickly but is treated easily through rehydration and antibiotics.