The US state of Florida declared an emergency Saturday as it braced for the arrival of tropical storm Fay, which swept through the Dominican Republic.

Four people in Haiti and the Dominican Republic died in flooding caused by the storm as it spun toward Cuba, the Miami Herald reported. Sustained winds of 75 kilometres per hour were recorded in the Dominican Republic.

The National Hurricane Centre in Miami said Fay could begin strengthening late Saturday or early Sunday and approach hurricane strength as it neared western Cuba.

Tropical storm warnings were already in place for Haiti, the Cayman Islands and Cuba, the statement said.

On Saturday evening, the storm's centre was about 96.5 kilometres south of Guantanamo in Cuba, and moving west. It had maximum sustained winds of 64 kilometres per hour. To become a hurricane, sustained winds must be at least 119 kilometres per hour .

Florida's governor Charlie Crist declared the emergency after forecasters said Fay could grow to a Category 1 hurricane before reaching the state as early as Monday, the Herald report said.

Authorities were preparing to evacuate residents living in low- lying areas and mobile homes.