Hurricane Irma, the most powerful Atlantic Ocean hurricane in recorded history, tore through a string of Caribbean islands Wednesday, knocking down buildings and disrupting power as it settled into a likely track for a weekend landing in southern Florida. At least three people are reported dead.

In St. Martin and St. Barthelemy, at least two people died and at least two others were seriously wounded, a spokesperson for France’s ministry for its overseas territories told ABC News. An infant died in Barbuda, where as many as 95% of structures were damaged, Prime Minister of Antigua and Barbuda Gaston Browne told CNN's "Anderson Cooper 360˚."

In Florida, South Carolina and Georgia, officials declared states of emergency and enacted defensive measures against a full onslaught from the 185-mph storm.

Florida Gov. Rick Scott activated 1,000 National Guard members as local authorities issued mandatory evacuation orders for the Florida Keys and low-lying areas on the mainland.

"We can rebuild your home, we can't rebuild your life," he cautioned anyone contemplating riding out Irma.

The governor warned Irma's unpredictable track could range from the Florida Panhandle to the East Coast and that the entire state should be prepared.

Scott emphasized Irma would be stronger and larger than Hurricane Andrew, the Category 5 storm that in 1992 killed 65 people in Florida, destroyed more than 63,500 homes and caused $26.5 billion in damage.

Evacuation orders for parts of Miami-Dade County, including Miami Beach, were set to take effect 7 a.m. Thursday. In the Florida Keys, orders took effect 7 p.m. ET Wednesday night and were set to take effect noon Thursday in Broward County.

In South Carolina, Gov. Henry McMaster declared a state of emergency. "We got this," McMaster said. "We can't stop the hurricane. If it comes, it's going to be here, but we can be ready for it."

Meanwhile, Florida officials worked to keep bottled water and fuel flowing into areas where local residents were either stocking up to stay or getting ready to pull out.

In Key Largo, Fla., a steady stream of vehicles, many towing boats, flowed off the Keys toward Miami Wednesday afternoon.

"People are pretty calm now that it's shifted a little bit more east, but everyone is still preparing," said gas station owner Ray Ochoa, 42.

Ochoa said his Key Largo Chevron station ran out of gas Tuesday, with high hurricane demand coming atop the traditionally heavy Labor Day end of the tourist season.

"It's a hell of a way to close out the season," he said, looking at his five plastic-wrapped pumps. He estimated he'll lose $6,000 in revenue a day by closing. "The sheriff told me there's no gas left on the Keys."

The pressure to take immediate safety measures built throughout Wednesday as Irma swept west out of the open Atlantic and chewed through a string of islands, including St. Martin, Barbuda, Anguilla and St. Barts.

Irma seemed likely to scrape the northern sections of the Dominican Republic, Puerto Rico and Cuba, while directly targeting the Bahamas, Virgin Islands and the Turks and Caicos Islands.

By 10 p.m. ET, Irma was about 70 miles north by northwest of San Juan, Puerto Rico, packing maximum sustained winds of 185 mph, according to the National Hurricane Center. It was moving toward the west-northwest at 16 mph.

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The U.S. State Department warned Americans to reconsider travel to Cuba, Haiti or the Dominican Republic due to the expected impact of the storm. U.S. Navy officials, however, decided not to evacuate the Naval Base at Guantanamo Bay, on Cuba's eastern tip, but did order an evacuation of non-essential personnel at Naval Air Station Key West.

Michel Magras, senator on the small French-speaking island of St. Barts, sent a text describing the "monster that passes over us," FranceInfo.com reported. "It is apocalyptic, a lot of damage, a lot of roofs torn off," he wrote.

On St. Martin, the half-French, half-Dutch island of around 80,000 people directly in the path of the storm, the relentless winds ripped off the roof of the main hospital.

French Interior Minister Gerard Collomb said government buildings on St. Martin had been destroyed, AFP reported.

"We know that the four most solid buildings on the island have been destroyed which means that more rustic structures have probably been completely or partially destroyed," he told reporters. The island prefect, an official appointed by France, and 23 staff took shelter in a concrete-lined room.

Previous hurricanes with Irma's ferocity, such as Hurricane Wilma in 2005 and Hurricane Mitch in 1998, reached maximum intensity in either the Gulf of Mexico or the Caribbean Sea.

"The chance of direct impacts from Irma beginning later this week and this weekend from wind, storm surge and rainfall continues to increase in the Florida Keys and portions of the Florida Peninsula," the National Hurricane Center said. "However, it is too soon to specify the timing and magnitude of these impacts."

President Trump has declared emergencies in Florida, Puerto Rico and the U.S. Virgin Islands, and authorities in the Bahamas said they would evacuate six southern islands.

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The U.S. Coast Guard strongly urged mariners to leave the Port of Key West, noting that it is safest when it has a minimum number of vessels. The Coast Guard ordered all oceangoing vessels and barges to head out to sea ahead of the onset of gale force winds.

It's been 25 years since a Category 5 hurricane struck the U.S., and Irma could potentially become just the fourth storm of that strength to barrel into the nation. Category 5 hurricanes destroy a high percentage of homes, often causing total roof failure and wall collapses. Fallen trees and power poles isolate residential areas. Power outages last for weeks or months. And areas can be uninhabitable for the same time frame.

"Watching Hurricane closely. My team, which has done, and is doing, such a good job in Texas, is already in Florida. No rest for the weary!" Trump tweeted Wednesday.

In addition to Irma, Hurricanes Katia and Jose formed on Wednesday. Katia is in the Bay of Campeche near Mexico, and should meander around for a few days before hitting the east coast of Mexico by the weekend. Jose is in the open Atlantic Ocean and could impact the Leeward Islands by the weekend.

This is the first time since 2010 that there have been three hurricanes at the same time in the Atlantic, according to Colorado State University meteorologist Phil Klotzbach.

Contributing: Trevor Hughes in Key Largo, Fla.