More than 1 million people in Puerto Rico -- nearly 70 percent of the Puerto Rico Electric Power Authority's customers -- are without power.
Puerto Rico Gov. Ricardo Rosello said "it will be difficult to estimate how long the power outage will last" until crews determine the extent of the damage.
Ports on the island remain closed, Rosello said, and it is unclear when commercial flights will resume. Schools and government offices are scheduled to reopen on Monday.
NASA shared this view of Hurricane Irma as it passed north of Hispaniola.
Hurricane Irma hits the Dominican Republic.
The National Hurricane Center (NHC) warned Thursday that the combination of a "life-threatening storm surge" and "large and destructive waves" will raise water levels far above normal tide levels in the Caribbean, and rainfall from Hurricane Irma could cause "life-threatening flash floods and mudslides."
Water levels could rise 15 to 20 feet above normal in the Turks and Caicos Islands and in the southeastern and central Bahamas, the NHC said.
Much of the Bahamas and the Turks and Caicos Islands will get eight to 12 inches of rain, with 20 inches possible in some areas. Some areas in the northern Dominican Republic and northern Haiti could see 15 inches of rain.
The eye of Hurricane Irma is moving west-northwest at 17 mph off the northern coast of Hispaniola as the Category 5 storm heads toward the Turks and Caicos Islands. The storm is located about 110 miles north of Punta Cana in the Dominican Republic and about 165 miles southeast of Grand Turk Island.
Irma carries maximum sustained winds of 180 mph, with higher gusts. Hurricane-force winds extend outward up to 50 miles from its center, and tropical storm-force winds extend up to 185 miles from its center.
"Hurricane conditions are expected to begin within the hurricane warning area in the Dominican Republic and Haiti today, with tropical storm conditions beginning in the next few hours," the NHC said. "Hurricane conditions are expected to begin in the warning area in the southeastern Bahamas and the Turks and Caicos Islands later today with tropical storm conditions expected within the next several hours."
Hurricane conditions will spread to the central Bahamas late Thursday or early Friday, the NHC said, and to the northwestern Bahamas Friday night and Saturday.
Cuba could also experience hurricane and tropical storm conditions on Friday.
Hurricane Irma has killed at least 10 people across the Caribbean Sea as the fearsome Category 5 storm continued hammering the islands there Thursday.
France’s interior minister on Thursday said that at least eight people had been killed and 23 more injured in the French Caribbean island territories.
Gerard Collomb added that the final death toll in Saint-Barthelemy and Saint-Martin could ultimately rise as rescue teams have not finished investigating the islands.
“It’s a tragedy, we’ll need to rebuild both islands,” he said during a news conference. “Most of the schools have been destroyed.”
Antigua and Barbuda Prime Minister Gaston Browne said a two-year old child was killed as a family tried escaping a damaged home during the storm.
“It is just really a horrendous situation,” he said after returning to Antigua after a plane trip to the neighboring island of Barbuda.
Browne said that Irma’s core crossed over Barbuda early Wednesday, leaving about 60 percent of its roughly 1,400 residents homeless.
The prime minister added that roads and telecommunications systems on both islands had been destroyed, meaning the recovery there would take months or even years.
One death was additionally reported in the nearby island of Anguilla, according to the Caribbean Disaster Emergency Management Agency.
Officials on Anguilla reported extensive damage to its airport, hospitals, shelters and school, adding that roughly 90 percent of roads there are impassible.
The U.S. National Hurricane Center predicted that Irma will remain a Category 4 or 5 hurricane for the next day or so as it passes just north of Haiti and the Dominican Republic Thursday.
Irma is expected to hit Florida sometime Sunday, and experts worry that it could strike the state’s entire coast from Miami to Jacksonville.
The storm then has the potential to barrel into the Carolinas and Savannah, Georgia, battering highly developed and populated areas there.
“This could easily be the most costly storm in U.S. history, which is saying a lot considering what just happened two weeks ago,” said Brian McNoldy, a hurricane researcher at the University of Miami, referencing last month’s Hurricane Harvey.
The Associated Press contributed to this report.