More than 200 people were killed, hundreds are missing and 100,000 were left homeless when Hurricane Georges struck the Dominican Republic last week. Most of the victims died in flooding or mudslides.
At the weekend, the United States Agency for International Development said the hurricane death toll in the Dominican Republic "is almost certain to exceed 500".
The US has shipped $500,000 (pounds 303,000) worth of supplies, including enough plastic sheeting to re-roof 15,000 homes.
Helicopter crews were hoping to reach San Juan de la Maguana, 120 miles west of the capital, Santo Domingo, where 76 bodies were recovered on Thursday. Half the town was under water or buried in mud.
In Cuba, where five people were killed in the storm and thousands left homeless, President Fidel Castro said the speedy evacuation of hundreds of thousands of people probably saved many more from dying during Georges' march across the island last Friday.