A woman walks through a flooded neighbourhood in Gonaives earlier in the week. (Ariana Cubillos/Associated Press)

Four tropical storms have wiped out most of Haiti's food crops and damaged irrigation systems and pumping stations, raising the spectre of acute hunger for millions in the impoverished country.

"The system of agriculture has been destroyed," Agriculture Minister Joanas Gue told the Associated Press. Aid agencies and diplomats also say Haiti desperately needs help to avert mass hunger.

Emergency aid has flowed in to people directly affected by Fay, Gustav, Hanna and Ike, storms that triggered flooding and killed at least 425 people in less than a month, including 194 in the critical rice-growing Artibonite Valley.

But the United Nations has raised less than two per cent of a critical $108 million US fundraising appeal, said Stephanie Bunker, a spokesperson for the world body's Office for the Co-ordination of Humanitarian Affairs.

Another $18 million US has been pledged but not delivered. And much more is needed, with farms damaged or destroyed across the poorest country in the Western Hemisphere.

"This will take billions of dollars. This is not something small," U.S. Agency for International Development Administrator Henrietta Fore told AP.

Refugees living in schools

Schools that were supposed to open in early September are still filled with refugees fighting over scraps of food aid.

Much of Gonaives, the nation's fourth largest city, remains flooded and without electricity. Malaria and other diseases are beginning to spread.

"The scope of this is frankly unimaginable in many countries," said U.S. Ambassador Janet Sanderson. "A lot of the progress of the last couple of years has been swept away by these waters."

The U.S. government is sending $29 million in food aid and humanitarian assistance, and countries like Colombia have airlifted food and clothing.

UN agencies have delivered food to more than 240,000 people, aided by soldiers of its 9,000-strong peacekeeping force and military ships like the USS Kearsarge and Canada's HMCS St. John's.

Haiti has always struggled to feed its people. Now, the task is getting to be impossible. On a helicopter tour on Tuesday, Fore saw that floodwaters still covered much of Haiti's rice-growing region.

Majority of harvest wiped out

Crops were covered with brown mud or lay crushed in ruined fields stretching as far as the eye could see.

Gue, the agriculture minister, estimates that 60 per cent of this year's food harvest has been wiped out by the storms, which hit just as farmers were preparing to collect corn, plantains and yams from their fields.

The fall rice harvest was lost as well. The damage could be felt for years —mountain topsoil, already loosened by rampant deforestation, washed out to sea.

Hundreds of irrigation basins, canals and pumping stations were damaged, and about 9,000 tonnes of discounted fertilizer distributed to farmers disappeared.

'Even before the storms, we were hungry' —Jacques-Eduoard Michele, who is struggling to find food.

Altogether, Gue estimated the storms caused $180 million in damage to Haiti's agricultural sector.

Food prices in some hard-hit cities have been pushed to even greater heights. After Ike, which brushed by Haiti on Sept. 7, the cost of U.S.-imported rice had doubled in Gonaives to $5.38 for a large can.

For millions of Haitians already facing malnutrition, a daily bowl of rice has become too expensive.

Jacques-Eduoard Michele's family used to depend on the rations of rice and plantains his father was paid to work in the Artibonite fields.

"Even before the storms, we were hungry," he said. "Now we are looking everywhere for food."

If the world does not respond with long-term aid, experts warn that deadly food riots could re-ignite, unravelling Haiti's fragile political stability.

"The situation is calm for now but it could easily erupt again," the Brussels-based International Crisis Group said this week.