A road is flooded during the passing of Hurricane Dorian in Freeport, Grand Bahama, Bahamas, Monday, Sept. 2, 2019. Dorian killed at least five people and caused "unprecedented" devastation in the Bahamas, the country's prime minister said. Photo: AP Photo/Tim Aylen.

Washington - Hurricane Dorian killed at least five people and caused "unprecedented" devastation in the Bahamas, the country's prime minister said Monday as the monster storm remained almost stationary over the two northern islands of the Caribbean chain for more than 30 hours.

Prime Minister Hubert Minnis gave an early accounting of the situation on Grand Bahama Island and the Abaco Islands at a news conference, saying his country was "in the midst of a historic tragedy."

Minnis said 21 other people had been injured and flown to a hospital in the capital Nassau, with five in serious condition. Search and rescue efforts were hampered by the storm Monday but would begin in earnest by Tuesday morning, he added.

Dorian was downgraded from a category 5 hurricane - the highest level - to a category 4 as it stalled over Atlantic Ocean archipelago, pummelling the islands with winds strong enough to rip the roofs off homes and topple trees, and a storm surge that brought intense flooding.

Videos posted on social media showed downed telephone poles, cars flipped over and massive waves crashing ashore in heavy rain in the Bahamas, an independent country within the British Commonwealth.

Dorian moved only about 10 kilometres in an eight-hour period, the National Hurricane Center (NHC) said in its 8 pm (0000 GMT Tuesday) update. Its eye was 40 kilometres north-east of Freeport and about 170 kilometres east of West Palm Beach, Florida, the centre added.

Dorian made landfall on the Abaco Islands on Sunday afternoon and churned as a category 5 storm until it was downgraded Monday, though it still had sustained wind speeds of 220 kilometres per hour.

The Miami-based NHC described Dorian as an "extremely powerful" storm in its 8 pm update. Forecasters expect it to turn toward the north-west by late Tuesday and move "dangerously close" to Florida's east coast through Wednesday evening.

Evacuation orders were posted for parts of coastal Florida as the NHC extended its storm surge warning northward into Georgia.

The potential storm surge of rising water moving inland from the coast could cause life-threatening inundations, the NHC said.

Florida Governor Ron DeSantis told a news briefing that people living in areas under evacuation orders should leave.

"Get out now while you have time, while there is fuel available and while you'll be safe on the roads," DeSantis said.