A suspected outbreak of cholera has killed at least 135 people in central Haiti, officials have said.
The director general of the health department, Dr Gabriel Thimote, said he was awaiting laboratory test results to confirm cholera was the cause.
The victims suffered diarrhoea, acute fever and vomiting. More than 1,500 people were infected, officials said.
The outbreak is centred in the Artibonite and Central Plateau regions, north of the capital Port-au-Prince.
Officials fear it could spread to the massive and tightly-packed displaced persons camps around the capital which still house tens of thousands left homeless by January's devastating earthquake.
Cholera is an intestinal infection caused by bacteria transmitted through contaminated water or food. The source of contamination is usually the faeces of infected people.
It causes diarrhoea and vomiting leading to severe dehydration, and can kill quickly if left untreated. It is easily treated though rehydration and antibiotics, however.
Car park treatment
Dr Thimote told Reuters news agency that of the 15 specimens so far tested, 13 led him to believe there was a cholera outbreak.
Health Minister Alex Larsen also said he believed it was cholera.
Dr Thimote said the worst-affected areas were Douin, Marchand Dessalines and areas around Saint-Marc, about 100km (60 miles) north of Port-au-Prince. Local hospitals were "overwhelmed", and a number of people were being evacuated to clinics in other areas, he added.
At one point on Thursday, hundreds of people laid in the car park of St Nicholas hospital in Saint-Marc, with intravenous drips in their arms to treat dehydration, until it began to rain and they were rushed inside.
Some patients said they drank water from a public canal, while others said they bought purified water.
"I ran to the bathroom four times last night vomiting," 70-year-old Belismene Jean Baptiste told the Associated Press.
Another man said three of his relatives had died within a matter hours.
David Darg, a medical relief worker in Haiti, told the BBC he had visited an area near Saint-Marc which - according to local residents - was the source of the outbreak.
"After visiting the hospital and meeting some of the medical staff, they were able to pinpoint where these cases were originating from so we headed out to a very rural area," Mr Darg told the BBC's World Today programme.
He said it was "an area that's popular for rice production".
"There's a lot of water in that area particularly. And we started heading out along narrow roads lined with villagers begging for water. Because by now they'd been seeing people dying in their communities and knew not to drink water from the river, which ordinarily would have been their main source of water. They drink water straight from the river," Mr Darg added.
The Pan American Health Organization (Paho) had sent two teams to the south of Artibonite, near Saint-Marc, a doctor with Paho told the BBC.
Pending the final test results, officials from Paho and the UN Office for the Co-ordination of Humanitarian Affairs (Ocha) attributed the deaths to "acute diarrhoea". They said they were concerned by the severity of the outbreak and the high number of reported deaths.
"Nothing can be verified at the moment. We have no numbers, no epidemiological data," said Dr Michel Thieren of Paho, adding that the symptoms could be associated with a number of underlying diseases.
Catherine Huck, deputy country director for the Ocha, said: "What we know is that people have diarrhoea and they are vomiting, and [they] can go quickly if they are not seen in time."
The victims range in age, but the young and the elderly appear to be the most affected.
There were fears of a cholera outbreak in the aftermath of January's earthquake, which killed some 250,000 people and left 1.5 million homeless.
Many people are still living in makeshift camps with unsanitary conditions and little access to clean drinking water, but there were no outbreaks, according to the World Health Organization (WHO).
The Artibonite department was not badly damaged in the earthquake but thousands of people who lost their homes have moved into camps or are living with relatives there.
"We have been afraid of this since the earthquake," said Robin Mahfood, president of Food for the Poor, which was preparing to airlift donations of antibiotics, oral dehydration salts and other supplies.