Irma âwill bring life-threatening wind, storm surge and rainfall hazardsâ to the northern coast of Hispaniola, which includes the Dominican Republic and Haiti, on Thursday, the Hurricane Center warned. It will pass directly over â or very near â the low-lying islands of Turks and Caicos, a British possession, and parts of the Bahamas on Thursday and Friday, the center forecast, and push a storm surge of seawater 15 to 20 feet high. The surge could put large parts of the islands under water.
Across the islands that were hit on Wednesday, people posted videos and photos online of the hurricaneâs fury: debris flying sideways in near-zero visibility, roofs ripped off structures, waves surging into buildings, downed trees and utility poles, and streets that had turned into raging currents carrying away cars and trucks.
The French interior minister, GÃ©rard Collomb, said the four sturdiest buildings on St. Martin had been destroyed, âwhich means that in all likelihood the more rustic buildings are probably totally or partially destroyed.â
With phone lines and electricity cut in many places, and roads impassable, President Emmanuel Macron of France and other officials said it was far too early to assess the true toll, in either lives or property.
The aftermath of the storm will be âharsh and cruel,â Mr. Macron said after a crisis meeting at the Interior Ministry in Paris. âWe will have victims to lament, and the material damage on the two islands is considerable.â
The devastating winds left many scrambling for safety.
Carmen Caballero, a 69-year-old retired doctor, was unsure at first whether to vacate her two-story home in San Juan, the capital of Puerto Rico. It is made of concrete, but has a metal roof that she feared might be ripped away. Then the power went out, the pelting rain and howling wind began, and she could hear debris crashing into things around her house and see tree branches falling into the streets.
She packed some water bottles, nuts, medicines, linens and other supplies in her car and drove to the shelter at the Roberto Clemente Coliseum. âAll my neighbors left too,â she said over the phone from there. âI wasnât going to stay alone in my house!â
In all, nearly 70 percent of households were without power and 17 percent of Puerto Rico was without water, Gov. Ricardo RossellÃ³ said on Thursday, but otherwise the island was largely unscathed.
âWe would like to start out thanking the Almighty,â Mr. RossellÃ³ said. âOur prayers were answered.â
On Culebra, a small, rustic Puerto Rican island east of the main island, JosÃ© PÃ©rez, the municipalityâs director of emergency management, took shelter with about 65 other people at a public high school Wednesday afternoon. Like many people there, he said, he lives in a wooden home.
âRight now we are feeling the fury of this hurricane,â Mr. PÃ©rez said in Spanish by phone. âI was 13 and I obviously remember Hurricane Hugo, but this is something incomparable. This is something terrible, an experience out of this world.â
Kelsey Nowakowski and some friends boarded up her house on St. Thomas, part of the United States Virgin Islands, and hunkered down, listening to the howling and thumping outside. âBased on the water we took in we think there is significant damage to the roof but donât think it blew off yet,â she said.
âWeâve all been in hurricanes before. There are five of us here, but have never felt anything like this before,â she added. âIt feels seismic, it feels catastrophic.â
Alex Woolfall, a British public relations consultant who was staying at the Westin resort on the Dutch side of St. Martin, posted a stream of alarming updates on Twitter while taking shelter with other guests in the hotelâs reinforced stairwell. He described âthunderous sonic boom noisesâ and the âscream of things being hurled against the building.â
âThis is like a movie I never want to see,â he wrote.
Throughout the region, communication was spotty at best; calls to people, businesses and government agencies â even the British Virgin Islands Department of Disaster Management â rang without being answered, or did not ring at all.
âStuff is flying around outside, and the visibility is down to about 20 to 30 feet, and we havenât hit the peak yet,â Gerry Yandel, executive editor of The Virgin Islands Daily News, said in the early afternoon. Two hours later, calls to the newspaper could not get through.
A JetBlue flight from San Juan to Fort Lauderdale, Fla., was canceled only after the passengers â many of them trying to get back to their homes in Florida â had checked out of hotels and gone to the airport. The 97 passengers were taken instead to the Clemente Coliseum, along with hundreds of others seeking shelter.
âTempers got a little heated; I had to control the situation,â said Carmen YulÃn Cruz, the mayor of San Juan. âThatâs like a spark in a gasoline tank. Five hundred people in one place: If one of them gets out of whack, it could have a ripple effect.â
She said the city was ready for whatever may come, having stockpiled fuel, ice and medication. The mayor said she, her family and their dogs would stay at the stadium, too.
âIf they get wet, I get wet,â she said.
Irma hit just days after Hurricane Harvey caused record flooding in Texas. With two other storms now reaching hurricane status â JosÃ©, trailing behind Irma, and Katia, in the Gulf of Mexico â meteorologists noted the unusual occurrence of three hurricanes forming at once in the Atlantic basin.
Hurricane Irmaâs maximum sustained winds of 185 m.p.h. have been matched by only three other Atlantic storms; the last, Hurricane Wilma, was in 2005. By Wednesday afternoon, Irma had kept that wind speed for over 24 hours, the longest period ever recorded.
The storm first made landfall on Barbuda about 2 a.m., then ripped across several more islands without losing intensity, traveling west-northwest. Puerto Rico was spared the worst of the stormâs wrath as it churned past in the evening. The center of the storm stayed about 50 miles north of the island.
Monroe County, which includes the Florida Keys, issued a mandatory evacuation order on Wednesday. Broward County, which includes Fort Lauderdale, advised people to evacuate some areas. In South Florida, which has millions of people and only two major highways, Interstates 95 and 75, to take people farther north, traffic and fuel shortages were already becoming problems as people tried to get out of the stormâs path.
Even so, more evacuation orders and advisories are expected in other parts of the region, and officials urged people to follow them, assuring the public that plenty of shelter space will be available.
âI cannot stress this enough,â Gov. Rick Scott said. âDo not ignore evacuation orders. We can rebuild your home but we cannot rebuild your life.â