(Reuters) - As Hurricane Sandy barreled toward the U.S. East Coast on Monday, the full extent of the storm's havoc on Haiti was just beginning to emerge.

Extensive damage to crops throughout the southern third of the country, as well as the high potential for a spike in cases of cholera and other water-borne diseases, could mean Haiti will see the deadliest effects of Sandy in the coming days and weeks.

Haiti reported the highest death toll in the Caribbean, as swollen rivers and landslides claimed at least 52 lives, according to the country's Civil Protection office. More than three days of constant rain left roads and bridges heavily damaged, cutting off access to several towns and a key border crossing with the Dominican Republic.

"The economy took a huge hit," Prime Minister Laurent Lamothe told Reuters. He also said Sandy's impact was devastating, "even by international standards," adding that Haiti was planning an appeal for emergency aid.

"Most of the agricultural crops that were left from Hurricane Isaac were destroyed during Sandy," he said, "so food security will be an issue."

Sandy also destroyed banana crops in eastern Jamaica as well as decimating the coffee crop in eastern Cuba.

But the widespread loss of crops and supplies in the south, both for commercial growers and subsistence farmers, is what has Haitian authorities and aid organizations had worried about most.

The past several months have seen a series of nationwide protests and general strikes over the rising cost of living. Even before Hurricane Sandy hit, residents complained that food prices were too high.

PEASANT CROP LOSSES

A rise in food prices in Haiti triggered violent demonstrations and political instability in April 2008. Jean Debalio Jean-Jacques, the Ministry of Agriculture's director for the southern department, said he worried that the massive crop loss "could aggravate the situation."

"The storm took everything away," said Jean-Jacques. "Everything the peasants had in reserve - corn, tubers - all of it was devastated. Some people had already prepared their fields for winter crops and those were devastated."

In Abricots on Haiti's southwestern tip, the community was still recovering from the effects of 2010's Hurricane Tomas and a recent dry spell when Sandy hit.

"We'll have famine in the coming days," said Abricots Mayor Kechner Toussaint. "It's an agricultural disaster."

The main staples of the local diet, bananas and breadfruit, were ripped out by winds and ruined by heavy rains.

In the southwestern Grand Anse department, a boat that regularly comes from Port-au-Prince to deliver supplies and pick up produce to sell in the capital had not come in more than a week because of the storm. The cost of basic things, like fuel, had already jumped.

In Camp-Perrin, a mountainous region in the southwest peninsula where Sandy's first fatality was recorded after a woman tried to cross a swollen river, coffee planters lamented the loss of a harvest they were weeks away from collecting.

"Coffee is the bank account of the peasants," said Maurice Jean-Louis, a planter and head of a coffee growers' cooperative in Camp-Perrin. Rain flooded many storage areas as well, soaking coffee beans that were set aside for export. He called the damage "incalculable."

CHOLERA IN THE CAPITAL

In the capital, Port-au-Prince, Sandy destroyed concrete homes and tent camps alike, where 370,000 victims of the 2010 earthquake are still living. Haitian authorities said 18,000 families were left homeless in the disaster.

Aid organizations began reporting a sharp rise in suspected cholera cases in several departments, with at least 86 new cases alone coming from Port-au-Prince's earthquake survivor camps, according to Dr. Juan Carlos Gustavo Alonso of the Pan American Health Organization. Many communities are still cut off and only accessible by helicopter, he said, so the broader rise in cholera was "still too early to tell."

Since October 2010, a cholera outbreak has sickened almost 600,000 people and killed more than 7,400 in Haiti.

Both the Haitian state and international aid organizations distributed food, water and other items to affected camps and communities throughout the weekend, including personal distributions by President Michel Martelly.

"These stocks are running dangerously low," said George Ngwa, spokesman for OCHA, a humanitarian coordinating body in Haiti. "After Tropical Storm Isaac in August, these stocks have not been replenished. What we're doing is scraping the bottom."

(Editing by David Adams, desking by G Crosse)