Hurricane Maria has knocked out power across the island of Puerto Rico, home to 3.5m people, officials have said.
Flash flood warnings cover the entire island, which continues to be lashed by heavy rain in the storm’s wake.
Meanwhile more pictures are emerging of widespread destruction on the small island of Dominica, hit on Monday.
Maria, now a category three storm, is now lashing the Dominican Republic further west and heading towards the Turks and Caicos Islands.
It is the second devastating storm to hit the Caribbean this hurricane season – the first being category five Irma earlier in September.
‘Our island destroyed’
Puerto Rico Governor Ricardo Rossello described the hurricane as “the most devastating storm in a century” and said that Maria had hit the island’s electricity grid so badly that it could take months to restore power.
The storm is being blamed for at least 10 deaths across the Caribbean. In Puerto Rico one man died after being struck by a board he had used to cover his windows.
The authorities have warned people to move to higher ground amid “catastrophic” flooding, and with up to 30 inches (76cm) more rain predicted by Saturday.
Images shared on social media show roofs being stripped away as winds as strong as 140 mph (225 km/h) whipped trees and power lines in Puerto Rico’s capital city, San Juan.
“God is with us; we are stronger than any hurricane,” Mr Rossello said. “Together we will rise again.”
The governor has asked President Donald Trump to declare the island a disaster area after the storm unleashed heavy flooding and life-threatening winds, and damaged infrastructure across the territory.
The US president is yet to do so, but has made federal emergency aid available.
At the scene: A city under curfew
By Will Grant in San Juan, Puerto Rico
After Hurricane Maria hit Puerto Rico – the biggest storm to make landfall on the island in almost a century – the governor of San Juan has ordered people to stay indoors between 18:00 and 06:00.
In part it is to protect people from accidents with so many electrical cables down and debris in the streets. Furthermore there are thousands of properties empty across the island after people sought refuge with family and friends or in emergency shelters.
Once the winds finally died down enough, residents ventured out to assess the damage. On first impressions, it seems the city has avoided widespread devastation but roofs have been ripped off homes, many trees are down, some balconies have fallen from the front of buildings and I saw at least one building that had completely collapsed near the waterfront.
The real question of how bad Maria has been for Puerto Rico will emerge as news comes in from the more remote regions. Thankfully though, it does seem there has been no major loss of life.
What happened in Dominica?
The storm has cut a swathe through the Caribbean on its north-westerly trajectory, hitting Dominica on Monday night.
It left at least seven people dead on the island, with some media reports putting the death toll at 24 or possibly higher.
Information on the true extent of the damage has been taking time to emerge as communications links were severely hit.
On Thursday CNN posted footage from a flight over the island showing scattered debris from homes ripped open and thousands of broken trees.
An adviser to Prime Minister Roosevelt Skerrit, Hartley Henry, said on Facebook: “The country is in a daze – no electricity, no running water – as a result of uprooted pipes in most communities and definitely [no] landline or cellphone services on island, and that will be for quite a while.”
Images from the capital, Roseau, show some streets knee-deep in debris.
Aid agencies have been preparing to go to Dominica to provide relief.
Hours before reaching Puerto Rico, Maria barrelled through the St Croix in the US Virgin Islands as a category five storm, sustaining winds of up to 175mph (281km/h).
The French territory of Guadeloupe suffered flooding on Monday and one person was killed by a falling tree and another died on the seafront. At least two others were missing after their ship sank near Desirade, the easternmost island in the archipelago.
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