At least 194 people have been killed in a cholera outbreak in Haiti, and health officials have warned the problem will likely get worse.
Rene Preval, the country's president, confirmed the outbreak on Friday and said the government was taking measures to try to stop the disease from spreading.
A state of emergency has been declared in the affected region and the rest of the country has been put on high alert.
More than 2,300 people have been rushed to hospital with severe diarrhoea, vomiting and dehydration in the last few days.
Medical facilities in the port city of Saint Marc have been overwhelmed, with hundreds of patients lying on blankets in a car park outside St Nicholas hospital with drips in their arms for rehydration.
Jon Arbus from the Pan American Health Organisation, speaking from Washington, DC, said the outbreak is expected to get much bigger.
"As we know from our experience, with situations of cholera where there is no infrastructure to deal with the crisis, it just gets much worse. We have to expect that and react to it."
Al Jazeera's Sebastian Walker, reporting from outside a hospital where about 1,400 people were seeking treatment, described the scene as "absolutely horrific".
"There was total chaos," he said.
"There were streams of patients arriving all the time being driven in from remote villages in the region, with severe cases of dehydration, acute diarrhoea and vomiting.
"We're hearing of cases all around the region we are in now. It's a rural region, the farming heartland of Haiti. There is a lot of poverty, high rates of unemployment, and there is very little drinking water available."
Our correspondent said the authorities' priority was to prevent the disease from spreading into camps where thousands of people left homeless by January's devastating earthquake are sheltering.
More than 250,000 people were killed in the earthquake and another 1.2 million were left homeless.
The Lower Artibonite region, where the outbreak is centred, did not experience significant damage in the quake but has absorbed thousands of refugees from the capital Port-au-Prince, 70km south of Saint Marc.
Aid groups have voiced concern for months that any outbreak of disease could spread rapidly in the country due to the unsanitary conditions in the makeshift camps housing the homeless, with little access to clean water.
Imogen Wall of the UN Office for the Co-ordination of Humanitarian Affairs said the UN's priority was to provide basic sanitation to help people get rehydrated.
"We're going to need a large public information aspect to this as well, to make sure people understand what they can do to protect themselves," she said. "That's going to be absolutely vital."
Victims ranged in age, but officials said the young and the elderly appeared to be the most affected.
The worst-affected areas were Douin, Marchand Dessalines and zones around Saint-Marc in the Artibonite region, according to government officials.
Gregory Hartl, a spokesman for the World Health Organisation, said it was not yet clear how widely the outbreak has spread and could spread.
"It's impossible to predict with any certainty that it will spread," he told Al Jazeera.
"We do know however that poor sanitation, poor infrastructure in terms of water provision, is one of the main ways that cholera does spread. Normally it spreads when feces gets back into the water system and people are forced to use water which hasn't been cleaned.
"Cholera has not been seen in Haiti for a long time, for about a century actually, so there is not a lot of experience on the part of the population and on the part of the the medical community within Haiti on how to treat this. So this is a big challenge in a number of ways."
Relief organisations were mobilising to ship medicine, water filtration units and other relief supplies to the Artibonite region.
"We have been afraid of this since the earthquake," Robin Mahfood, the president of Food for the Poor, said while the group was preparing to airlift donations of antibiotics, oral dehydration salts and other supplies.
The outbreak is being blamed on the Artibonite river, an artery crossing Haiti's rural centre that thousands of people use for much of their daily activities from washing to cooking.
Charles Henry Baker, a presidential candidate, travelled to the stricken area and pleaded for help.
"The situation is terrible. Inside the hospital, they're overcrowded. They're not overcrowded, it's beyond
overcrowded," he said.
"They need some field hospitals put up as quickly as possible to be able to take in the amount of
people they have. They need doctors. They need nurses. People are all over, on the floor, the way it was after the 12th of January [earth quake]. We need help; we need quick help."
Cholera is transmitted by water but also by food that has been in contact with unclean water contaminated by cholera bacteria.
It causes serious diarrhoea and vomiting, leading to dehydration. The disease is easily treatable by rehydration and antibiotics, but with a short incubation period, it can be fatal if not treated in time.
The World Health Organisation defines cholera as "an extremely virulent disease. It affects both children and adults and can kill within hours".
The impoverished Caribbean nation has also been hit in recent days by severe flooding, adding to the misery of those struggling to survive in the scores of tent cities now dotting the country.
Reconstruction has barely begun despite billions of dollars pledged for Haiti in the wake of the disaster. Less than 15 per cent of money promised at a UN donor's conference in March has been delivered.