Hurricane Dorian caused limited damage in the northern Caribbean as it left the region and gathered strength late Wednesday, setting its sights on the U.S. mainland as it threatened to grow into a Category 3 storm.

Power outages and flooding were reported across the U.S. Virgin Islands, the British Virgin Islands and the Puerto Rican islands of Vieques and Culebra after Dorian hit St. Thomas as a Category 1 storm.

"We're happy because there are no damages to report," Culebra Mayor William Solis told The Associated Press, noting that only one community lost power.

Meanwhile, Dorian caused an island-wide blackout in St. Thomas and St. John in the U.S. Virgin Islands, and scattered power outages in St. Croix, government spokesman Richard Motta told the AP. In addition, the storm downed trees and at least one electric post in St. Thomas, he said, adding that there were no reports of major flooding so far.

"We are grateful that it wasn't a stronger storm," he said.

There were no immediate reports of damage in the British Virgin Islands, where Gov. Augustus Jaspert said crews were already clearing roads and inspecting infrastructure by late Wednesday afternoon.

The U.S. National Hurricane Center said the storm could grow into a dangerous Category 3 storm as it pushes northwest in the general direction of Florida.

Here are the 11 PM AST/EDT August 28 Key Messages for Hurricane <a href="https://twitter.com/hashtag/Dorian?src=hash&ref_src=twsrc%5Etfw">#Dorian</a>. For more information see: <a href="https://t.co/tW4KeFW0gB">https://t.co/tW4KeFW0gB</a> <a href="https://t.co/0M1r9waE3l">pic.twitter.com/0M1r9waE3l</a> —@NHC_Atlantic

"This will be a large storm approaching the Southeast," said NHC meteorologist Dennis Feltgen.

At 11 p.m. ET, Dorian was 145 kilometres north of San Juan, Puerto Rico with maximum sustained winds of 140 km/h while moving northwest at 20 km/h.

People in Florida were starting to get ready for a possible Labour Day landfall, with county governments along the state's east-central coast distributing sandbags and many residents rushing to warehouse retailers to load up on water, canned food and emergency supplies.

"All Floridians on the East Coast should have 7 days of supplies, prepare their homes & follow the track closely," Florida Gov. Ron DeSantis said in a tweet.

He declared a state of emergency Wednesday afternoon for counties in the storm's path.

As Hurricane <a href="https://twitter.com/hashtag/Dorian?src=hash&ref_src=twsrc%5Etfw">#Dorian</a> approaches, I’ve declared a state of emergency to ensure local governments and emergency management agencies have ample time, resources and flexibility to get prepared. Please continue to follow local reports and <a href="https://twitter.com/FLSERT?ref_src=twsrc%5Etfw">@FLSERT</a> for updates. <a href="https://t.co/FyQM6wd8er">https://t.co/FyQM6wd8er</a> —@GovRonDeSantis

"Because of the uncertainty in the track of this storm, every resident along the East Coast needs to be ready," said Jared Moskowitz, director of Florida's Division of Emergency Management, in a statement.

The latest, still-uncertain extended forecast shows the storm's sustained winds could grow to about 185 km/h before landfall.

Puerto Rico seemed to be spared any heavy wind and rain, a huge relief to many on an island where blue tarps still cover some 30,000 homes nearly two years after Hurricane Maria. The island's 3.2 million inhabitants also depend on an unstable power grid that remains prone to outages since it was destroyed by Maria, a Category 4 storm.

Dorian prompted U.S. President Donald Trump to declare an emergency Tuesday night and order federal assistance for local authorities.

A reported 990 customers were without power across Puerto Rico by late Wednesday afternoon, according to Angel Figueroa, president of a union that represents power workers.

Police said an 80-year-old man in the northern town of Bayamon died on Wednesday after he fell trying to climb up to his roof to clear it of debris ahead of the storm.

Category 1 strength winds bend palm trees as Hurricane Dorian slams into St. Thomas, U.S. Virgin Islands Wednesday in this still image taken from social media video. (Cassandra Crichlow/Reuters)

Trump sent a tweet assuring that "We are tracking closely tropical storm Dorian as it heads, as usual, to Puerto Rico. FEMA and all others are ready, and will do a great job."

He added a jab at Puerto Rican officials who have accused the government of a slow and inadequate response to Hurricane Maria.

I said yesterday that Trump needs to be quite, “calm down” get out of the way and make way for those of us who are actually doing the work on the ground. Maybe Trump will understand this time around THIS IS NOT ABOUT HIM; THIS IS NOT ABOUT POLITICS; THIS IS ABOUT SAVING LIVES. <a href="https://t.co/uy5dZY9uwY">https://t.co/uy5dZY9uwY</a> —@CarmenYulinCruz

The mayor, Carmen Yulin Cruz, tweeted that Trump needs to "calm down get out of the way and make way for those of us who are actually doing the work on the ground."

Dorian earlier caused power outages and downed trees in Barbados and St. Lucia.

Although top government officials in Puerto Rico said they were prepared for the storm and had sufficient equipment, a couple of mayors, including those in the western region, said they did not have enough generators or shelters that were properly set up.

Learned Maria's lesson, governor says

Jose Ortiz, executive director of Puerto Rico's Electric Power Authority, acknowledged that the distribution system still has weak areas and could "suffer" under high winds. However, he stressed the agency has the needed inventory, including more than 120,000 lights, 23,000 poles and 7,400 transformers.

But Freddyson Martinez, vice-president of a power workers' union, told The Associated Press that while the electric grid has improved in some areas, he worries about a lack of power line workers and post-Maria patches which feature lines affixed to palm trees.

Officials in Puerto Rico said public schools and government offices would remain closed through at least Thursday.