The “monster” storm struck the island yesterday at 6.15am local time (11.15am BST) and was the strongest hurricane to hit Puerto Rico for almost a century.
Doors have been ripped from their hinges and roofs torn from homes across the island, with the extent of the damage still not fully realised.
Abner Gómez, head of the disaster management agency, said none of the customers of Puerto Rico's Electric Power Authority had any electricity.
Mr Gómez told local media: "When we are able to go outside, we are going to find our island destroyed.
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GETTY•REUTERSPuerto Rico has been left without power as Hurricane Maria devastated the island
"It's a system that has destroyed everything in its path.”
Flooding has devastated the island too, with some of Puerto Rico’s main rivers breaking their banks as the storm hit and leaving entire streets under water.
Roads have been strewn with debris and fallen power lines and trees lie across the US territory as authorities try to assess the extent of the damage.
Puerto Rico Governor Ricardo Rossello confirmed that one man was killed when the storm struck after he was hit by flying debris.
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Hurricane Maria pummels storm-ravaged Puerto Rico
EPAA shattered bus stop lies in the road as the damage wreaked by Maria is slowly revealed
When we are able to go outside, we are going to find our island destroyed
Mr Rossello issued a curfew shortly after Maria hit in a bid to protect local residents from accidents with so many electrical cables down and debris in the streets.
Despite the one confirmed fatality, it appears Puerto Rico escaped any major loss of life.
The category 3 storm brought torrential rain and heavy winds as it passed around 50 miles north of Punta Cana on the Dominican Republic’s northern coast with maximum sustained winds of 115 miles per hour (185 km/h), according to the National Hurricane Center.
Punta Cana was hit with winds of 58 mph (93 kph) and Maria was forecast to bring storm surges of up to 6 feet (1.83 m) in the Dominican Republic, leading to major flooding fears particularly after the devastation witnessed on its southern neighbour, Puerto Rico.
The heavy rain poured down streets across the island, prompting flash flood warnings while trees were brought down which made some areas virtually inaccessible.
REUTERSA banana plantation lies in tatters
Maria will then move towards the