Hurricane Irma has torn off roofs and knocked out all electricity on the French islands of Saint Martin and Saint Barthelemy in the Caribbean.
France has requisitioned planes and sent in emergency food and water rations.
The regional authority for Guadeloupe and neighbouring islands said that the fire station in Saint Barthelemy is under 3ft of water and no rescue vehicles can move.
It said the government headquarters in Saint Martin have been partially destroyed and the island is in a total blackout.
Electricity is also partially down on the larger island of Guadeloupe, where the threat receded despite danger of heavy flooding.
French minister for overseas territories Annick Girardin expressed fear "for a certain number of our compatriots who unfortunately didn't want to listen to the protection measures and go to more secure sites".
"We're preparing for the worst."
Antigua and Barbuda prime minister Gaston Browne said his twin-island nation appears to have weathered its brush with Hurricane Irma.
He said there were no deaths in Antigua and preliminary reports indicated there were no deaths in Barbuda despite widespread reports of damaged buildings and downed trees. He said he plans to visit as soon as possible.
Hurricane Irma is roaring along a path pointing to Puerto Rico, the Dominican Republic, Haiti and Cuba before possibly heading for Florida over the weekend.
The eye of the storm passed over Barbuda at around yesterday morning, the US National Weather Service said.
Heavy rain and howling winds raked the neighbouring island of Antigua, sending debris flying as people huddled in their homes or government shelters.
Officials warned people to seek protection from Irma's "onslaught" in a statement that closed with "May God protect us all".
The most dangerous winds, usually nearest to the eye, were forecast to pass near the northern Virgin Islands and near or just north of Puerto Rico on Wednesday.
US president Donald Trump declared emergencies in Florida, Puerto Rico and the US Virgin Islands, and authorities in the Bahamas said they would evacuate six southern islands.
The northern Leeward Islands were expected to see normal tide levels rise by as much as 11ft while the Turks and Caicos Islands and south-eastern Bahamas could see a surge of 20ft and higher waves later in the week, forecasters said.
Bahamas prime minister Hubert Minnis said his government was evacuating six islands in the south because authorities would not be able to help anyone caught in the "potentially catastrophic" wind, flooding and storm surge. People there would be flown to Nassau in what he called the largest storm evacuation in the country's history.
"The price you may pay for not evacuating is your life or serious physical harm," Mr Minnis said.
The US National Weather Service said Puerto Rico had not seen a hurricane of Irma's magnitude since Hurricane San Felipe in 1928, which killed a total of 2,748 people in Guadeloupe, Puerto Rico and Florida.
"The dangerousness of this event is like nothing we've ever seen," Puerto Rico governor Ricardo Rossello said.
"A lot of infrastructure won't be able to withstand this kind of force."
The director of the island's power company has warned that storm damage could leave some areas without electricity for about a week to as long as six months.
The eye of the storm was expected to rip westward on a path taking it a little north of Puerto Rico, the Dominican Republic, Haiti and Cuba.
In Florida, people stocked up on drinking water and other supplies.
Florida governor Rick Scott activated 100 members of the Florida National Guard to be deployed across the state, and 7,000 National Guard members were to report for duty on Friday when the storm could be approaching the area. On Monday, Mr Scott declared a state of emergency in all of Florida's 67 counties.
Officials in the Florida Keys geared up to get tourists and residents out of Irma's path, and the mayor of Miami-Dade County said people should be prepared to evacuate Miami Beach and most coastal areas.
