A monster storm with sustained winds near 260kph that has killed at least 47 people, Ivan sent sea water surging over the low-lying Caymans, a British territory and wealthy offshore finance centre of 45,000 people.
Forecasters said the rare and deadly Category 5 hurricane was expected to pass near or over extreme western Cuba on Monday evening. They warned of a 6-7.6 metre storm surge of seawater to the east of where the centre makes landfall in Cuba.
On Grand Cayman, the largest of the three Cayman Islands, homes and businesses were flooded, an airport runway was submerged and roofs were torn off, witnesses said.
Panicked residents climbed on kitchen worktops to escape a waist-high storm surge that swept at least 1km inland.
Ham radio operators reported that people were standing on rooftops, the US National Hurricane Center said. There were no immediate reports of casualties in the Caymans, but Ivan killed 19 people in Jamaica when it brushed past on Friday night and Saturday.
While damage was extensive, the island of 2.7 million people appeared to have escaped the total havoc wrought on Tuesday on the tiny spice island Grenada, where 19 people died and 90% of buildings were flattened or badly damaged.
The deadly hurricane is rated
Ivan was headed for tobacco-growing regions of western Cuba or Mexico's Yucatan Peninsula on Monday and then towards the United States, where it could inflict a third hurricane strike on Florida within a month or curve west towards New Orleans.
The hurricane's path was unclear, and the most powerful winds around its eyewall could end up closer to the Yucatan than to Cuba as it sweeps into the Gulf of Mexico and makes an expected northerly turn.
In southern Florida - storm-weary after a visit from Hurricane Charley on 13 August and Hurricane Frances a week ago - homeowners began to breathe a sigh of relief after it appeared the vulnerable Florida Keys would likely be spared.
Nevertheless, state officials warned that at least 1.7 million people living in fragile mobile homes or low-lying areas were at risk along Florida's Gulf Coast.
"We really have to err on the side of caution," said Florida state meteorologist Ben Nelson. At least 12,000 Jamaicans spent Sunday night in shelters after huge waves, flash floods or fierce winds wrecked their homes. Looting, which erupted as the storm hit, appeared under control, as heavily armed police patrolled.
Ivan may be the third hurricane
to hit Florida within a month
Cuba evacuated 1.3 million people - more than a tenth of its population - and prepared for 30cm of rain.
Mexico's Yucatan peninsula also braced for possible high winds, and began evacuating 12,000 residents and tourists from Isla Mujeres, a resort island 13km from Cancun.
On Saturday, Ivan's top sustained winds were reported at 265kph, making it the sixth-strongest Atlantic storm recorded in the Atlantic basin, the hurricane centre said.
Ivan was downgraded to Category 4 on the five-step Saffir-Simpson storm scale as it hit the Caymans, but strengthened again to a rare Category 5 on Sunday night.