Hurricane Wilma has strengthened to an "extremely dangerous" category 5 hurricane, with sustained maximum winds of 175 mph, the National Hurricane Center (NHC) has said.
Projections for Wilma's path suggest that the storm may skirt the western tip of Cuba on Friday before curving eastward towards Florida.
Forecasters warn that the storm could possibly slam into southwestern Florida by this weekend.
A category 5 hurricane can cause a storm surge of more than 18 feet above normal.
The NHC said: "All interests in the Florida Keys and the Florida peninsula should closely monitor the progress of Wilma."
Wilma is the 21st named storm of the 2005 hurricane season and the 12th to reach hurricane status. Of those, five have developed into major hurricanes.
