Large trees and poles crashed down in Kingston on Friday, some hitting houses. Ravines running through the city quickly overflowed and flooded streets.
Huge waves pounded the coast around St Thomas in the south-east of the island and a storm surge tore away at least two houses, the Caribbean Disaster Emergency Response Agency said. Elsewhere, the surge washed away roads.
"It's extremely windy. The whole island is without electricity," said Joseph Robinson, 45, from the British Caribbean territory of Turks and Caicos, as he took shelter in the lobby of a Kingston hotel. "It's going beyond manageable."
Ivan, which has already killed 27 people as it has rampaged across the Caribbean, strengthened when it reached Jamaica with winds of 250kph, just short of qualifying as a rare, top-level Category 5 hurricane for the second time since it formed.
Large waves have pounded the
coast of the island
If it continues on its present path it could be the third big storm in a month to slam into Florida.
In the Cayman Islands, a British territory west of Jamaica, the authorities told coastal dwellers to flee battering waves and a 2.4-metre storm surge.
In the Florida Keys, long lines of tourists and residents streamed out of the 160-km island chain as Floridians, already bruised by hurricanes Charley and Frances in the past four weeks, wearily prepared for a possible third strike in an unusually busy Atlantic storm season.
Bracing for worst
In the immediate path of Ivan, Jamaica's 2.7 million people braced for the worst. "It is clear that the severity of this hurricane will have extremely serious effects, as predicted," said Jamaican Prime Minister PJ Patterson as he declared a state of emergency.
Half a million Jamaicans - over one-sixth of the population - were urged to evacuate low-lying areas as Ivan approached. But many held out, vowing to protect their homes from looters.
As fierce winds lashed Kingston, robbers held up emergency workers at gunpoint. A doctor was shot and taken to hospital. By 11pm EDT (0300 GMT), Ivan's centre was about 55km south of Kingston at latitude 17.5 north and longitude 76.9 west, the US National Hurricane Centre said.
It was moving west to north-west at 17kph. Hurricane-force winds extended for 95km from the centre.
Half a million Jamaicans have
been urged to evacuate
Security forces from Grenada and other Caribbean countries secured buildings in the capital, St George's, while residents on foot or in cars with smashed windshields searched for scarce water, food and petrol.
Authorities said 90% of Grenada's homes were damaged when the hurricane hit on Tuesday and issued an urgent appeal for tents, tarpaulins, cots, blankets and building supplies to shelter 60,000 of the volcanic island's 90,000 people.
Tour groups joined forces to evacuate tourists to Barbados while the US State Department said it would evacuate American citizens on Saturday.
In addition to 17 deaths in Grenada and one in Jamaica, four people died in Venezuela, four in the Dominican Republic and one in Tobago.