Haiti started burying some of its dead in mass graves in the wake of Hurricane Matthew, a government official said on Sunday, as cholera spread in the devastated southwest and the death toll from the storm rose to 1,000 people.

The powerful hurricane, the fiercest Caribbean storm in nearly a decade, slammed into Haiti on Tuesday, whipping it with 145 mile-per-hour (233 kph) winds and torrential rains.

A Reuters tally of numbers from local officials showed that 1,000 people were killed by the storm in Haiti, the poorest country in the Americas.

The official death toll from the central civil protection agency is 336, a slower count because officials must visit each village to confirm the numbers.

Authorities had to start burying the dead in mass graves in Jeremie as the bodies were starting to decompose, Kedner Frenel, the most senior central government official in the Grand'Anse region on Haiti's western peninsula.

Frenel said 522 people died in Grand'Anse alone. A tally of death reported by mayors from 15 of 18 municipalities in Sud Department on the south side of the peninsula showed 386 people there. In the rest of the country, 92 people died, the same tally showed.

Frenel said there was great concern about the cholera spreading, and that authorities were focused on getting water, food and medication to the thousands of people living in shelters.

Cholera causes severe diarrhea and can kill within hours if untreated. It is spread through contaminated water and has a short incubation period, which leads to rapid outbreaks.

Government teams fanned out across the hard-hit southwestern tip of the country over the weekend to repair treatment centers and reach the epicenter of one outbreak.