|Camp residents reinforced their tents as Hurricane Tomas approached the Caribbean nation [Reuters]
Hurricane Tomas has swamped coastal towns in Haiti, and drenched crowded camps for survivors of January's earthquake.
The centre of the storm cleared Haiti's northern coast on Saturday, but heavy rain has triggered flooding and landslides that have killed at least seven people.
More than a million Haitians, living in makeshift camps since the January earthquake, have been told to leave their tents.
But Al Jazeera's Sebastian Walker, reporting from the capital, Port-au-Prince, said only a small number of people had been able to move to any kind of more sturdy accommodation.
"The vast majority are still in the camps, sheltering in makeshift accommodations which really won't stand up to any extreme weather," he said.
"The lucky ones who were actually given somewhere else to go are sheltering in old hospitals, schools, churches - really anything that is still standing after the January earthquake."
Walker said the worst danger is going to be flash floods and mudslides triggered by the rains.
"For a period of about 12 hours, we've had constant rainfall ... It seems that we have avoided the worst-case scenario of a direct hit of the hurricane on Port-au-Prince. We are hearing it's passing now to the west, out at sea."
UN agencies were on a "war footing" because "half a million people at least will be affected" by Tomas, Elisabeth Byrs, a spokeswoman for the UN Office for Co-ordination of Humanitarian Affairs, said..
Al Jazeera's Sebastian Walker reports on the hurricane crisis from a makeshift camp in Port-au-Prince
The government said it had taken steps to accommodate as many as 100,000 people in schools, churches and hospitals.
Jean-Max Bellerive, the prime minister, went on national radio to urge citizens to leave the zones at risk.
"There will be rain and wind throughout the country. Don't be stubborn. Leave if you are in a fragile shelter," he said.
But many were reluctant to leave the camps, worried that if they leave the overcrowded camps, they will lose their only home and few possessions.
Natacha Jean was refusing to leave the Corail-Cesselesse camp, one of the largest in the Port-au-Prince region.
"We're not leaving. No one can make us. We have been here for eight months, and we won't abandon our tent," she said. "Where would we go?"
The UN said the hurricane will almost certainly exacerbate a cholera epidemic that has so far killed 442 people and sickened more than 6,700, according to government figures.
"Although the cholera outbreak has largely been contained to regions north of Port-au-Prince... Tomas could set back our efforts to contain the outbreak in the camps, as heavy rains cause pooling water that can increase spread of the disease," the American Red Cross said.
Tomas swept across the Caribbean's eastern islands as a hurricane during the weekend, killing at least five people in St Lucia. Several more people were missing.
With the storm threat and the spreading cholera epidemic, Haiti faces major disruption less than a month before November 28 presidential and legislative elections. But electoral officials have not moved to postpone the vote.