A UN official said the 'biggest fear is people being caught by high waters' when Tropical Storm Tomas strikes [AFP]

After struggling for weeks to contain a cholera epidemic, Haiti is bracing for the arrival of a tropical cyclone that threatens hundreds of thousands of people with deadly floodwaters, a United Nations official has said.

Citing government estimates, Nigel Fisher, the UN humanitarian co-ordinator in Haiti, said on Wednesday that Tropical Storm Tomas is expected to strike on Friday and could unleash torrential rains and a storm surge of up to six to nine feet (2-3 metres) that will put 1.5 million people at risk.

The storm, which has killed at least a dozen people in St Lucia and lashed Barbados in the last few days, will likely worsen the cholera epidemic that has already killed more than 440 people, Fisher said.

"The biggest fear is people being caught by high waters and the potential spread of cholera," Fisher said.

"People should [not] be under the misapprehension that it [the epidemic] is under control. The cholera epidemic is likely to spread."

The outbreak of the diarrhoeal disease has triggered another national emergency in the Western Hemisphere's poorest nation.

It came as the deforested and mountainous land, which is very vulnerable to flash floods and mudslides, was still struggling to recover from a January 12 earthquake that killed more than a quarter of a million people.

About 1.3 million quake survivors are still living in fragile outdoor camps.

Al Jazeera's Craig Mauro, reporting from the Haitian capital Port-au-Prince near a camp housing people displaced by the earhtquake, said: "There are more than a million people living in this camp and telling them that they should, if they have any way of doing it, take shelter in the homes of friends and relatives ... [is] a dire warning for people who already have next to nothing and are living under tarpaulin and tents. They, of course, will be the most vulnerable if a severe storm passes through here."

Tomas has a terrifying potential to add to the country's misery and is seen gathering force again to start battering Haiti and Jamaica from Thursday night, forecasters said.

"Hurricanes never come at a good time but we are particularly stretched right now," Fisher said.
   
The worst fear is a hurricane-strength storm that hits multiple regions simultaneously, overwhelming the capacity of the government and the aid community to cope, he said.

"The big challenge is saving lives. If the hurricane is so huge that all over the country is hit severely ... we will really be stretched and we will have to make difficult choices about where to put scarce assets," he added.