MIAMI -- Hurricane Irma hurtled through the Caribbean on Friday, leaving catastrophic damage in its wake as it closed in on Florida where it could slam into Miami this weekend.
The storm barreled between southeastern Cuba and the Turks and Caicos Islands early Friday morning, and is expected to move westward toward central Cuba and the Bahamas.
Irma was downgraded to an "extremely dangerous" Category 4 storm on Friday, with winds reaching a sustained maximum of 155 mph, the U.S. National Hurricane Center said. At its peak, winds reached sustained maximums of 180 mph.
At least 10 people were killed as Irma pummeled small northeastern Caribbean islands such as Barbuda and St. Martin/St. Maarten. In Puerto Rico, hundreds of thousands people were left without power.
The Red Cross estimates that 1.2 million people have already been battered by the storm and warned that it poses a serious threat to millions more.
Irma is expected to remain at least a Category 4 hurricane until landfall in Florida this weekend, the U.S. National Hurricane Center said.
It issued hurricane and storm surge warnings for South Florida on Thursday night. Mandatory evacuations have been issued for many counties in South Florida, where residents have begun a mass exodus.
Around 3 a.m. MDT, Irma's center was about 55 miles northwest of Great Inagua Island in the Bahamas, moving west-northwest with maximum sustained winds of 155 mph. Hurricane-force winds could be felt as far as 70 miles from the center.
Irma is forecast to move toward the southeastern Bahamas on Friday morning, then heading between the north coast of Cuba and the Bahamas in the next day or two.
Irma left at least 10 people dead, including four on St. Martin, four in the U.S. Virgin Islands, one on Anguilla, and one on Barbuda, officials said.
Hurricane warnings are in effect for parts of Cuba, Haiti, the Turks and Caicos Islands, and the southeastern, central and northwestern Bahamas.
The Red Cross said as many as 26 million people could be exposed to destructive winds and torrential rain just in the Dominican Republic, Haiti and Cuba.
Hurricane and storm surge warnings are also in effect for South Florida, extending from Jupiter Inlet on the east coast of the state, southward around the Florida Peninsula to Bonita Beach on the west coast.
The hurricane warning included the Florida Keys, Lake Okeechobee and Florida Bay.
The Bahamas, a nation of about 390,000, ordered evacuations ahead of Irma's arrival 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.
Irma, which at its peak sustained maximum wind speeds of 180 mph for longer than any storm ever recorded in the Atlantic basin, brought heavy rain and powerful winds overnight to the low-lying Turks and Caicos Islands.
Residents of the islands, a British overseas territory with a population of about 35,000, were told to stay put.
"Fifteen roofs have come off and there's damage to part of the roof of the hospital," Gov. John Freeman said.
He said there was "quite a bit of damage" in the capital island of Grand Turk.
The U.K. Foreign Office said officials on the islands were working intensively on disaster preparedness and response.
In Puerto Rico, about 56,680 customers were without water, with the island's northeast hit the hardest, according to Jesus Poupart of the emergency operations center.
Irma is expected to bring massive rainfall, which could cause flash floods and mudslides in parts of Puerto Rico, the Virgin Islands, Dominican Republic, Haiti, Turks and Caicos islands, the Bahamas and Cuba, as well as the U.S.
The Caribbean islands already pummeled by Irma have begun assessing the damage, finding shredded buildings, battered cars and streets submerged in water.
Barbuda is barely habitable, with about 95 percent of its buildings damaged, Prime Minister Gaston Browne said late Wednesday.
Barbuda, which has 1,800 residents, is one of two major islands in the nation of Antigua and Barbuda. Browne estimated the damage will cost $100 million to fix.
"It looks like (a) garbage disposal," said Marlon Carr, a photographer who toured the island. "There was rubble and roof galvanized all over the island. It looked like some of the houses ... were imploded on."
Witnesses told him of "40-foot containers flying, animals flying" during the storm, he said.
Irma's eye passed directly over Barbuda on Wednesday and now the northeastern Caribbean nation is anxiously watching Hurricane Jose to the east, which has strengthened to a Category 3 storm.
Antigua and Barbuda are under a hurricane watch for Jose, which could pass close to those islands Saturday. The government has called for voluntary evacuations from Barbuda, Browne said.
The island of St. Martin was also badly hit, with about 50 people reported injured as well as the four killed.
Dutch Prime Minister Mark Rutte said the looting situation in St. Maarten, the Dutch portion of St. Martin island, was "serious" in the wake of the hurricane, a spokesman for his office said.
Local authorities, in collaboration with the Dutch military, are restoring order on the island, the spokesman said.
The airport in St. Maarten has reopened for military use only, with military aircraft focused on bringing help and personnel to the island, he added.
France's overseas territories minister, Annick Girardin, also confirmed looting in the French portion of the island, St. Martin.
"Our worst fears have played out in Barbuda and elsewhere," said Walter Cotte, the regional director for the Americas for the Red Cross.
"We can't yet assess the full extent of damage, but we expect that the Red Cross will be delivering extensive support to many thousands over the coming weeks and months."