Hurricane Dorian, a category one storm, is bearing down on Puerto Rico, which is still recovering from its ravaging by Hurricane Maria two years ago.
US forecasters said Dorian could make landfall on the populous eastern side of the US territory on Wednesday.
Dorian is then projected to head for the US, possibly making landfall in eastern Florida as a category three hurricane.
US President Donald Trump has been criticising Puerto Rico.
What’s the forecast?
The storm is packing winds of over 75mph (120 km/h) and is expected to bring up to 10in (25cm) of rain in some places.
Wind gusts of 111mph (178 km/h) have been reported as of Wednesday afternoon, local time, close to St Thomas as the hurricane’s eye passed near the island.
Forecasters have warned of life-threatening flash flooding, surf and rip current conditions as the storm moves across the islands.
The National Hurricane Center (NHC) says Dorian will approach the eastern coast of Florida next Monday.
Schools on Puerto Rico are closed and there are fears of power cuts. Two cruise liners have adjusted their itineraries to avoid the territory.
What did President Trump say?
Late on Tuesday, President Trump approved an emergency declaration authorising federal agencies to provide disaster relief.
He also lashed out at Puerto Rico as the island hunkered down for Dorian’s approach.
In a series of tweets on Wednesday, he said the island’s government was “broken” and “corrupt”.
He added that he was “the best thing that’s ever happened to Puerto Rico”.
Carmen Yulin Cruz. mayor of the Puerto Rican capital San Juan, tweeted: “THIS IS NOT ABOUT POLITICS; THIS IS ABOUT SAVING LIVES.”
On Tuesday, Mr Trump tweeted: “Wow! Yet another big storm heading to Puerto Rico. Will it ever end?”
The president has previously faced political censure for his 2017 response to Hurricane Maria.
He rated his handling of the disaster as a “tremendous success” while disputing official findings of the spiralling death toll.
Has Puerto Rico recovered from Maria?
Some 30,000 homes in Puerto Rico still do not have proper roofs, merely tarps, according to US media.
The territory remains burdened with more than $70bn in debt – a crisis exacerbated by storms.
Nearly 3,000 of the island’s over three million residents died as a result of Maria – many due to poor healthcare and a lack of electricity and clean water.
More than 1,000 roads remain blocked by that storm’s landslides, the island’s transportation secretary has said.
It took 11 months to restore full power to the island, and recurring electricity cuts caused further deaths from diabetes and sepsis.
The storm was the most intense cyclone worldwide that year and caused an estimated $100bn (£77bn) in damage.