By Steve Almasy and Faith Karimi, CNN

(CNN) -- As Hurricane Irma's eye roars away from the tiny island of Barbuda and toward St. Martin, residents along its path scrambled to evacuate while stocking up on water, food and gas.

The massive eye stared down on Barbuda early Wednesday, thrashing it with howling winds before it marched along its path on the Caribbean.

Irma's eye was bigger than Barbuda, CNN meteorologist Jenn Varian said. It packed winds of 185 mph, making it one of the most powerful Atlantic storms ever recorded.

The Category 5 hurricane is "potentially catastrophic," especially if it hits islands at high tides, the National Hurricane Center said.

Latest developments

-- Islands near its expected path Wednesday morning and early afternoon include St. Martin, Anguilla, St. Kitts and Nevis, and the British and US Virgin Islands.

-- The storm's center is expected to pass near or just north of Puerto Rico on Wednesday afternoon or night.

-- Irma then is expected to turn toward the Turks and Caicos islands and the southeastern Bahamas, where storm surges of up to 20 feet are possible, the hurricane center said.

-- It's too early to tell whether it will make landfall on the US mainland, but forecasts show it could churn toward Florida over the weekend.

-- Floridians are not sitting around, waiting. Evacuations are underway, with some schools shut down and shelters set up.

-- In the US Virgin Islands, Gov. Kenneth E. Mapp ordered a 36-hour curfew that was starting at 6 a.m. local time Wednesday.

-- In the Bahamas, emergency evacuations have been ordered for six southern islands -- Mayaguana, Inagua, Crooked Island, Acklins, Long Cay and Ragged Island.

-- "This is the largest such evacuation in the history of the country," Prime Minister Hubert Minnis said.

-- Bahamian officials also canceled vacation time for police and defense forces.

-- Meanwhile, Tropical Storm Jose, in the open Atlantic far to the southeast of Irma, is expected to become a hurricane by Wednesday night.

-- "Interests in the Leeward Islands should monitor the progress of Jose," the National Hurricane Center said.

Islands under hurricane warning

Forecasters are mostly concerned about the northeastern Caribbean, according to Michael Brennan of the hurricane center.

Islands under hurricane warning include Anguilla, Antigua, Barbuda, Puerto Rico, the US and British Virgin Islands, Montserrat, St. Kitts and Nevis, Saba, St. Eustatius, St. Martin/St. Maarten, St. Barts, the Dominican Republic from Cabo Engano to the northern border with Haiti, Guadeloupe, the southeastern Bahamas and the Turks and Caicos Islands.

"The extremely dangerous core" of Irma was to move over parts of the northern Leeward Islands on Wednesday morning, near or over parts of the northern Virgin Islands later Wednesday and near or just north of Puerto Rico Wednesday afternoon or Wednesday night, the hurricane center said.

Puerto Rico: Long lines

Puerto Rico Gov. Ricardo Rosselló declared a state of emergency and has activated the National Guard.

For hours, people lined up outside hardware stores, hoping to get plywood, batteries and power generators. If Irma knocks out power, Puerto Ricans said it could take weeks or months before it is restored.

Last month, the director of Puerto Rico's power utility, Ricardo Ramos Rodríguez, said several factors have made the island's electric system "vulnerable and fragile," CNN affiliate WAPA reported.

One of those is the shortage of employees. Many workers recently retired or left their jobs for better prospects on the US mainland, Ramos Rodríguez said.

Evacuations set for Florida

Jimmy Brumbaugh packed up his family in their RV and left Astatula, Florida, for Georgia. As he headed out of town, he posted a picture showing a long line of cars, waiting to get gas.

"People are genuinely scared down here," he said. "... We are dead center in the state, but I'm not taking any chances. I also don't want to put my family through the misery of riding out the storm. We've done it before, and it's horrible."

In Eustis, northwest of Orlando, Pat Arnold and her husband took precautions in case Irma hit.

"My husband and I prepared for Irma by getting some cash out, fueling cars and filling gas cans with nonethanol gas (for use with our chainsaw if needed), ... and making sure we have enough batteries, canned food, etc," she told CNN.

From Miami Beach to Ocala, Floridians braced for the storm, with some posting images of empty shelves at local grocery stores.

Miami-Dade County will start evacuating special-needs residents Wednesday, and may announce other evacuations soon, Mayor Carlos Gimenez said.

Schools and county offices will be closed Thursday and Friday.

Monroe County, which includes the Florida Keys, was ordering visitors to evacuate by sunrise Wednesday, and residents should begin to evacuate 12 hours later.

After declaring a state of emergency across Florida, Gov. Rick Scott said President Donald Trump had "offered the full resources of the federal government."

Scott also ordered 7,000 National Guard troops to report for duty by Friday morning.

"Learn your evacuation zone. Listen to your locals," he said. "This storm has the potential to devastate this state. You have to take this seriously."