Hurricane Dennis lashed into the Florida Keys Saturday, flooding streets and downing power lines.

The storm was headed to the Gulf Coast, where 1.4 million residents were under evacuation orders.

Given a category three designation, the hurricane had maximum sustained winds of 185 km/h and wasgathering strength.

In the southern tip of Florida, more than 211,000 homes and businesses lost power.

The impact was severe in Key West, where fallen branches, street signs and other debris littered the streets. The popular tourist destination, Duval Street, was under 46 cm of water.

Gulf Coast residents, meanwhile, were bracing for the storm, which was expected to hit the coast of the Florida Panhandle, Alabama or Mississippi on Sunday.

In Alabama, about 500,000 people were under evacuation orders, as were 700,000 in Florida and 190,000 in Mississippi.

Highways were jammed as people fled inland from the coasts of Florida, Alabama and Louisiana.

Dennis is the strongest Atlantic hurricane to form so early in the season since records began in 1851. The season runs from June 1 to Nov. 30.

The hurricane was responsible for 20 deaths in Haiti and Cuba earlier this week.

It struck Cuba with such ferocity on Friday, President Fidel Castro described it as "diabolical."

Dennis is following the path of Hurricane Ivan, which struck last year and caused 29 deaths and $4 billion US damage in the Panhandle alone.

That hurricane along with two others tore through the Caribbean in 2004, killing hundreds of people and causing billions of dollars in damage.

Hardest hit was Haiti, which is vulnerable to flash floods and mudslides. Last year, about 60,000 people died in floods in May and September.