The "extremely dangerous" Category Four storm was set to stampede just south of the Florida Keys on Tuesday with winds near 135 miles (215 kilometers) per hour, the US National Hurricane Center (NHC) said, prompting a mandatory phased evacuation order for the islands.

Residents stocked up on drinking water, batteries and gasoline, and most shops were shuttered along Route 1, the overseas highway that joins the Keys like a string of beads out to this southernmost city in the United States.

"We've learned from the past. They're so fickle," Rob Mitchell, owner of Keys Divers snorkeling outfit in Key Largo, said of the storms that batter southern Florida -- the latest of which tore through the state in late August and killed 11 people.

"It can be aiming right away from you, and all of a sudden turn," Mitchell said after securing his 40-foot boat, which normally carries visitors to nearby reefs.

As he spoke, residents and visitors retreated north on the narrow strip of highway, appearing to heed the evacuation order.

Even skirting the Keys on Tuesday, Ike would likely bring life-threatening rip currents and torrential rains, forecasters warned, and on Sunday President George W. Bush declared a state of emergency for Florida.

The NHC projected a pounding for Cuba Sunday night, when Ike will likely hit near Guantanamo and then barrel westward across the island through Monday and turn northwest into the Gulf of Mexico.

Some Floridians were taking a wait-and-see approach. In Key West, where residents are known for their laid-back, independent streak, many said they would stay put.

Jacqueline Sands, general manager of the Ernest Hemingway Museum, said she would ride out the storm like she always does: babysitting the 49 cats that live on the grounds of the famous writer's old home. Some are said to be descendants of Hemingway's pets.

"There's no way we would leave the cats behind. We never abandon them," said Sands.

In Miami, hardware stores did a brisk business in last-minute supplies.

"Plywood, propane canisters, tiki torches," said Home Depot department manager Andrew Neunie, rattling off items most in demand.

"People are coming out and taking care of what they need to take care of."

Densely populated south Florida, including the cities of Miami and Fort Lauderdale, has not been hit by a major hurricane since Hurricane Andrew in 1992, which was the costliest disaster in US history until it was overtaken by Hurricane Katrina in 2005.

The center of Ike was forecast to miss greater Miami -- population 2.5 million -- but forecaster Cristina Carrasco of the Miami-based NHC warned against complacency.

"Miami is still on the corner of the (forecast) cone, so we're still watching it very closely," Carrasco told AFP.

"Any little movement to the north could bring it on top of us."