© AFPHaitian refugees await word of Caribbean storm Tomas at a tent city in Port-au-Prince
Haiti reeled from a spike in cholera deaths as authorities planned mass evacuations from squalid tent cities ahead of a major storm set to lash the Americas' poorest nation beginning Thursday.

Tropical Storm Tomas was barreling toward Haiti, threatening a direct hit early Friday as a hurricane bringing "life-threatening flash floods and mudslides over mountainous terrain," according to the US National Hurricane Center (NHC).

A hurricane warning was issued, which means hurricane conditions are expected in the affected area within 24 to 36 hours, while tropical storm-force winds and rain were expected to buffet the Caribbean nation from late Thursday.

"These conditions make outside preparations difficult or dangerous, and preparations to protect life and property should be rushed to completion," the Miami-based center warned.

To communicate his sense of urgency, President Rene Preval set out on a nationwide tour to get people living in high-risk areas to evacuate, as authorities closed schools and urged locals to relocate to safer ground.

"We have decided to shut schools temporarily ahead of the storm, because some of them will be used for shelters," explained Miloudy Vincent, a top aide to the education minister.

But it won't be easy: some of the 1.3 million already displaced residents of tent cities do not want to leave without guarantees of safe shelter.

At one of the largest camps, Corail Cesselesse, residents were already gearing up to protest Thursday against being forcibly relocated.

Much of Haiti's population of just under 10 million is vulnerable and exposed in a country dominated by mountainous erosion-prone terrain. Many live beside rivers, their main water source, but risk being swept away in storms.

International partners raced to get much-needed supplies, as US naval commanders ordered the USS Iwo Jima to Haiti with humanitarian aid.

The amphibious ship is equipped with 10 helicopters and a crew of 1,600, including medical and engineering teams ready to assist in relief efforts after the storm strikes.

A cholera epidemic meanwhile is spreading in unsanitary camps for people still homeless after the massive earthquake that struck the impoverished nation in January. The epidemic has claimed 442 lives so far, with a total of 6,742 cases.

At 0600 GMT, Tomas was churning in the Caribbean about 490 kilometers (305 miles) southwest of Port-au-Prince with maximum sustained winds of 75 kilometers (45 miles) per hour, the NHC said, noting the storm would strengthen further until it likely becomes a hurricane on Friday.

It was moving in a northwesterly direction at 11 kilometers (seven miles) per hour but was expected to turn to the north and northeast toward Haiti.

A hurricane watch was in effect for the southeastern Bahamas and the Turks and Caicos Islands, while tropical storm watches were issued for parts of the Dominican Republic -- which shares Hispaniola island with Haiti -- Jamaica and Cuba.

Tomas was expected to dump as much as 38 centimeters (15 inches) of rain over the Dominican Republic and Haiti.

Haiti's poor infrastructure was likely to exacerbate any hit from Tomas, and has already been blamed for worsening health hazards.

There namely are not enough ambulances to bring people to hospital during the cholera outbreak, which is threatening some 25,000 new mothers and their babies in and around the capital, according to international aid group Save the Children.

The World Health Organization has warned the outbreak is far from over and Haiti should prepare for the "worst-case scenario" -- cholera in the capital.