Santo Domingo, Dominican Republic - At least 22 people died and more than 6,000 were displaced due to the effects of Tropical Storm Gustav in Haiti and the Dominican Republic, authorities said Wednesday.

Gustav made landfall in Haiti on Tuesday as a hurricane, but weakened and was downgraded to a tropical storm early Wednesday, with sustained winds of 95 kilometres per hour and higher gusts, the Miami-based US National Hurricane Centre said.

The storm was expected to pass between Jamaica and the south- eastern coast of Cuba on Thursday and "could regain hurricane strength within the next day or two."

As it swept the Dominican Republic, the storm left eight people dead following a mudslide that buried a home in Santo Domingo. Authorities said 5,425 people were displaced from their homes and more than 1,000 homes were damaged.

At least 14 people were killed in Haiti and more than 1,000 families had to be evacuated from their homes.

Beginning early Wednesday, troops of the United Nations Stabilization Mission in Haiti, and Haitian Civil Protection officers were patrolling affected areas and distributing water and food.

Gustav is expected to dump 15 to 30 centimetres of rain over Haiti, eastern Cuba, Jamaica and the Cayman Islands, the hurricane centre said and this rain "will likely produce life-threatening flash floods and mud slides."

In the United States, authorities warned residents to be prepared for a possible landfall in coming days, but noted it was too soon to know where the storm might come ashore after crossing the Gulf of Mexico.

"We are continuing to monitor this storm as state government agencies, including the state police and the Louisiana National Guard, have been put on standby so we are ready to quickly respond if the storm heads our direction," Louisiana Governor Bobby Jindal said.

Three years ago Hurricane Katrina devastated New Orleans and much of the Gulf Coast in the state and neighbouring Mississippi, leaving more than 1,800 people dead.

Tropical Storm Gustav had driven up the price of crude oil on fears it could impact oil platforms in the Gulf of Mexico, Bloomberg financial news reported.

Last week, Tropical Storm Fay left 11 people dead and caused substantial damage to agriculture in Haiti and the Dominican Republic.

Gustav is the seventh storm in the current north-Atlantic hurricane season, which officially finishes at the end of November.