SAN JUAN, P.R. — Hurricane Irma struck the northeast Caribbean with terrifying force Wednesday, its battering rain and winds of up to 185 miles per hour leaving a trail of chaos, wreckage and flooding from Barbuda to Puerto Rico, before taking aim at islands farther west and, beyond them, Florida.
Already one of the most powerful storms ever recorded, Irma could become one of the most destructive as well, depending on its path, and officials from Turks and Caicos to Florida pleaded with people to heed advisories to evacuate to shelters and higher ground. The National Hurricane Center described the hurricane as “potentially catastrophic.”
The storm made direct hits on Barbuda, St. Barthélemy, St. Martin, Anguilla and the British Virgin Islands, and raked the United States Virgin Islands and Puerto Rico with hurricane-force wind and torrential rain. Gaston Browne, prime minister of Antigua and Barbuda, said Irma had destroyed 95 percent of the structures on Barbuda, an island with about 1,600 people.
The authorities confirmed that the hurricane had killed at least one person in Antigua and Barbuda; one on Anguilla, a British possession; and two in French territory, which includes St. Barthélemy and the northern part of St. Martin. Another died in Puerto Rico while preparing for the storm.
Irma “will bring life-threatening wind, storm surge and rainfall hazards” to Puerto Rico on Wednesday and to the northern coast of Hispaniola, which includes the Dominican Republic and Haiti, on Thursday, the Hurricane Center warned. It will pass directly over — or very near — 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 hurricane’s 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, Gérard Collomb, said the four sturdiest buildings on St. Martin had been destroyed, “which means that in all likelihood the more rustic buildings are probably totally or partially destroyed.”
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 “harsh and cruel,” Mr. Macron said after a crisis meeting at the Interior Ministry in Paris. “We will have victims to lament, and the material damage on the two islands is considerable.”
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. “All my neighbors left too,” she said over the phone from there. “I wasn’t going to stay alone in my house!”
On Culebra, a small, rustic Puerto Rican island east of the main island, José Pérez, the municipality’s 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.
“Right now we are feeling the fury of this hurricane,” Mr. Pérez said in Spanish by phone. “I was 13 and I obviously remember Hurricane Hugo, but this is something incomparable. This is something terrible, an experience out of this world.”
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. “Based on the water we took in we think there is significant damage to the roof but don’t think it blew off yet,” she said.
“We’ve all been in hurricanes before. There are five of us here, but have never felt anything like this before,” she added. “It feels seismic, it feels catastrophic.”
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 hotel’s reinforced stairwell. He described “thunderous sonic boom noises” and the “scream of things being hurled against the building.”
“This is like a movie I never want to see,” he wrote.
Throughout the region, communication was spotty at best; calls to people, businesses and government agencies — even the British Virgin Islands Department of Disaster Management — rang without being answered, or did not ring at all.
“Stuff is flying around outside, and the visibility is down to about 20 to 30 feet, and we haven’t hit the peak yet,” 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 — many of them trying to get back to their homes in Florida — 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.
“Tempers got a little heated; I had to control the situation,” said Carmen Yulín Cruz, the mayor of San Juan. “That’s 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.”
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.
“If they get wet, I get wet,” she said.
Irma hit just days after Hurricane Harvey caused record flooding in Texas. With two other storms now reaching hurricane status — José, trailing behind Irma, and Katia, in the Gulf of Mexico — meteorologists noted the unusual occurrence of three hurricanes forming at once in the Atlantic basin.
Hurricane Irma’s 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 storm’s 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 storm’s 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.
“I cannot stress this enough,” Gov. Rick Scott said. “Do not ignore evacuation orders. We can rebuild your home but we cannot rebuild your life.”