In the town of Kay Coq on the remote island of Ile-à-Vache, a fishing community of 2,000 people about six miles off the coast of Les Cayes, the hurricane left a scene of chaos.

“Right now there is no more Kay Coq,” said Carobert Altema, 58, a fisherman. “Houses are down, people are screaming. We have no updates about which people are missing.”

Mr. Altema said household belongings had been washed out to sea. “At my age, this is the first time I have experienced something like this,” he said.

Aid organizations in Haiti said rescue efforts were focused on evacuating people from houses threatened with collapse.

“People have been leaving their homes under the full force of the storm to find shelters,” said Jean-Claude Fignole, a program manager in Haiti for Oxfam, the international charity.

Mr. Fignole said the storm had hit Haiti just as farmers in the south were about to harvest plantains, a staple in their subsistence diet. “There will be real hunger in the weeks ahead,” he said.

Image Hurricane Matthew appeared to have largely spared Port-au-Prince, the capital, with few signs of the flooding elsewhere. Credit... Carlos Garcia Rawlins/Reuters

Other charitable groups doing work in Haiti also expressed alarm about the storm’s effect on food production in the country, which has been struggling to recover from a prolonged drought.

John Hasse, national director for World Vision Haiti, said that the storm destroyed avocado trees and that at least two communities had lost their entire banana crops.

“We have gotten good rain this year. We were starting to see progress in malnutrition,” he said, because families were able to prepare healthier food for their children. “We think this is going to destroy a lot of it.”

The National Hurricane Center had projected 15 to 25 inches of rain for southern Haiti and in the southwestern part of the Dominican Republic, warning that as much as 40 inches of rain might fall in some areas.

Some streets in Port-au-Prince flooded, and public transit was paralyzed. But by late afternoon, the storm appeared to have spared Port-au-Prince the worst of its wrath. Moderate rain was falling, residents reported, with no sign of the catastrophic flooding that was affecting areas farther south.

Although the sea level rose at the edge of Cité Soleil, the city’s harbor slum, the water did not breach the central wharf. Residents in the most vulnerable part of the slum, a low-lying shantytown called Deye Chabon, piled logs and garbage into barricades that kept the water from spilling into the narrow streets.

Nonetheless, residents of Deye Chabon were keeping a wary eye on the sea. “They say if it keeps rising, they will have to go find another place to be,” said Sherby St. Louis, 16, a student.

Melanie Jean Pierre, 32, a street vendor, said she was riding out the storm in Port-au-Prince with her children. She said the only damage had come from a leak in the roof that soaked her bed.