Authorities have urged people to stock up on food and water and secure their homes. Thousands are still living in tents following a huge earthquake in 2010.
The mayor of Haiti's largest slum in the capital Port-au-Prince, Frederic Hislain, called on the government to evacuate some 150,000 people whose homes are threatened.
Haitian officials say that about 1,300 emergency shelters have been built, enough to accommodate 340,000 people. Both airports in Haiti are closed.
But some Haitians have refused to go to shelters, fearful of having their possessions stolen.
One local in Port-au-Prince, however, said the community would unite in the face of the storm's danger.
"We are communicating amongst ourselves thanks to our own means. We will tell the people how the situation is. If things are bad then we will come together.