The eye of Hurricane Irma passed over Barbuda around 1.47 am, the National Weather Service said.
Irma was maintaining category five strength with sustained winds near 185 mph (295 kmh), the US National Hurricane Centre said.
The storm bought fierce winds, surf and rain to the Leeward Islands on Wednesday.
"We are hunkered down and it is very windy... the wind is a major threat," said Garfield Burford, the director of news at ABS TV and Radio on the island of Antigua, south of Barbuda.
"So far, some roofs have been blown off."Here are the latest estimates of when tropical-storm-force winds could arrive & are most likely to arrive with #Irmahurricanes.gov11:23 PM - Sep 5, 201753 1,519 891 NHC Atlantic Ops@NHC_AtlanticMost people on Antigua and Barbuda were without power and 1,000 people on Antigua were spending the night in shelters, Burford reported.
"It's very scary ... most of the islands are dark so it's very, very frightening," he said.
Irma is currently heading through the Caribbean towards Florida and may make landfall there at the weekend, but its precise path is uncertain.
The most dangerous winds are forecast to pass near the northern Virgin Islands and near, or just north, of Puerto Rico.
Hurricane warnings are in place on several islands, including Anguilla, Montserrat, St. Kitts and Nevis, the U.S. and British Virgin Islands, Puerto Rico and the Dominican Republic.
Category 5 #Irma with 185-mph winds-#Hurricane preparations in the NE Leeward Islands should be nearing completion hurricanes.gov7:23 PM - Sep 5, 201760 1,461 1,028 NHC Atlantic Ops@NHC_AtlanticTourists in the area were evacuated on Tuesday before the hurricane arrived.
British Airways sent an empty aircraft to the region, bringing 326 customers back to the UK, and a Virgin Atlantic flight left Antigua five hours early to avoid the storm
The Foreign and Commonwealth Office said Britons should follow the advice of local authorities and any evacuation orders.
Hurricane Irma is a category five storm. Pic: @NHC_Atlantic
President Donald Trump has declared emergencies in Florida, Puerto Rico and the US Virgin Islands.
If it hits Florida it will be the second powerful storm to hit the US mainland in two weeks after Hurricane Harvey caused widespread devastation and killed around 60 people.
Bahamas prime minister Hubert Minnis has said the government will evacuate six southern islands as authorities would not be able to help people caught in the "potentially catastrophic" conditions there.