Relief officials reported scenes of utter ruin in parts of the Bahamas Tuesday and rushed to deal with an unfolding humanitarian crisis in the wake of Hurricane Dorian, the most powerful storm on record ever to hit the islands. At least seven deaths were confirmed by the prime minister, with the full scope of the disaster still unknown.

The storm's punishing winds and muddy brown floodwaters destroyed or severely damaged thousands of homes, crippled hospitals and trapped people in attics.

"It's total devastation. It's decimated. Apocalyptic. It looks like a bomb went off," said Lia Head-Rigby, who helps run a local hurricane relief organization and flew over the Bahamas' hard-hit Abaco Island. "It's not rebuilding something that was there; we have to start again."

She said her representative on Abaco told her that "there's a lot more dead" and that the bodies were being gathered up.

Emergency authorities, meanwhile, struggled to reach victims amid conditions too dangerous even for rescue workers, and urged people to hang on.

Volunteers rescue several families from the rising waters of Hurricane Dorian in Freeport Tuesday. (Ramon Espinosa/The Associated Press)

"We wanted to go out there, but that's not a risk we're capable of taking," Tammy Mitchell of the Bahamas' National Emergency Management Agency told radio station ZNS Bahamas. "We don't want people thinking we've forgotten them.... We know what your conditions are. We know if you're stuck in an attic."

After practically parking itself over the Bahamas for a day and a half, Hurricane Dorian finally started a slow move away from the islands Tuesday afternoon, but not before unleashing a catastrophic onslaught.

Dangerous winds and life-threatening storm surges were forecast to continue through the evening, according to the U.S. Naitonal Hurricane Center.

"We are in the midst of a historic tragedy," Prime Minister Hubert Minnis said. "The devastation is unprecedented and extensive." He said he feared the death toll would climb.

Late Tuesday, Dorian was centred about 155 kilometres east of Cape Canaveral, Florida, and it was moving northwest at 9 km/h. Hurricane-force winds extended up to 95 kilometres from its centre, while tropical storm-force winds could be felt up to 280 kilometres from the core.

New Watches and Warnings Issued Along the Southeastern United States Coast. Rain and Wind Threat also Increasing For Portions of Virginia Coast and Southern Chesapeake Bay. Here are the 5 PM Tuesday Key Messages for <a href="https://twitter.com/hashtag/Dorian?src=hash&ref_src=twsrc%5Etfw">#Dorian</a>. For More Info See: <a href="https://t.co/tW4KeGdBFb">https://t.co/tW4KeGdBFb</a> <a href="https://t.co/yBpORo5H9O">pic.twitter.com/yBpORo5H9O</a> —@NHC_Atlantic

The storm was expected to continue its approach toward the Florida coast late Tuesday through Wednesday evening, very near the Georgia and South Carolina coasts Wednesday night and Thursday, and near or over the North Carolina coast late Thursday and Thursday night.

Hundreds of thousands of people in those states were ordered to evacuate before the storm rolls up the Eastern Seaboard, bringing the possibility of life-threatening storm-surge flooding even if the storm's heart stays offshore, as forecast. Several large airports announced closures and many flights were cancelled for Monday and Tuesday.

Food, clean water will be needed: aid officials

In the Bahamas, the U.S. Coast Guard airlifted at least 21 people injured on Abaco Island, which Dorian hit on Sunday with sustained winds of 295 km/h and gusts up to 220 mph 355 km/h, a strength matched only by the Labour Day hurricane of 1935, before storms were named.

Watch as injured people are transported to Nassau via U.S. Coast Guard helicopter

The U.S. Coast Guard airlifted at least 21 people injured on Abaco Island in the Bahamas to the capital, Nassau, as Hurricane Dorian battered the country. 0:53

Red Cross spokesperson Matthew Cochrane said more than 13,000 houses, or about 45 per cent of the homes in Grand Bahama and Abaco, were believed to have been severely damaged or destroyed. United Nations officials said more than 60,000 people on the hard-hit islands will need food, and the Red Cross said some 62,000 will need clean drinking water.

"What we are hearing lends credence to the fact that this has been a catastrophic storm and a catastrophic impact," Cochrane said.

Watch as a woman offers a first-hand account of the storm from Freeport:

Kimberly Mullings tells CBC News about how people are trapped in their homes in Freeport, Bahamas. 1:20

Scientists say climate change generally has been fuelling more powerful and wetter storms and the only recorded storm more powerful than Dorian was Hurricane Allen in 1980, with 305 km/h winds, though it did not make landfall at that strength.

Duane Sands, the Bahamas health minister, told The Associated Press that Dorian devastated the health infrastructure in Grand Bahama island and massive flooding has rendered the main hospital in Marsh Harbor unusable.

He said the building is intact and sheltering 400 people, but needs food, water, medicine and surgical supplies. He also said crews are trying to airlift between five and seven end-stage kidney failure patients from Abaco who haven't received dialysis since Friday.

Cars sit submerged in water from Hurricane Dorian in Freeport on Tuesday. Dorian was beginning to inch northwestward after being stationary over the Bahamas, where its relentless winds have caused catastrophic damage and flooding. (Ramon Espinosa/The Associated Press)

A spokesperson for the UN World Food Program said Tuesday that a team is ready to help the Bahamian government assess storm damage and prioritize needs. Herve Verhoosel said preliminary calculations show 45,700 people on Grand Bahama island may need food, along with another 14,500 on the Abaco islands.

Bahamian officials said they received a "tremendous" number of calls from people in flooded homes. One radio station said it received more than 2,000 distress messages, including reports of a five-month-old baby stranded on a roof and a woman with six grandchildren who cut a hole in a roof to escape rising floodwaters. At least two designated storm shelters flooded.

Here are the most likely times of arrival of tropical-storm-force winds from <a href="https://twitter.com/hashtag/Dorian?src=hash&ref_src=twsrc%5Etfw">#Dorian</a> in the next 3 days: <br><br>-E-Central and NE Florida Coast Tonight<br>-Georgia Coast Wednesday<br>-South Carolina Late Wednesday<br>-North Carolina Thursday<br><br>Please prepare accordingly! <a href="https://t.co/tW4KeGdBFb">https://t.co/tW4KeGdBFb</a> <a href="https://t.co/KH5cVtuUUc">pic.twitter.com/KH5cVtuUUc</a> —@NHC_Atlantic

Minnis said many homes and buildings were severely damaged or destroyed, but it was too early to say how much the rebuilding effort would cost. Choppy brown floodwaters reached roofs and the top of palm trees on Monday.

Dorian also killed one person in Puerto Rico, at the start of its path through the Caribbean.

U.S. coastal areas prepare

A mandatory evacuation of entire South Carolina coast took effect Monday covering about 830,000 people, and transportation officials reversed all lanes of Interstate 26 from Charleston to head inland earlier than planned after noticing traffic jams from evacuees and vacationers heading home on Labour Day, Gov. Henry McMaster said.

A few hours later, Georgia Gov. Brian Kemp ordered mandatory evacuations for that state's Atlantic coast, also starting at midday Monday.

The coastline from north of West Palm Beach, Florida, through Georgia was expected to get eight to 15 centimetres of rain, with 23 centimetres in places, while the Carolinas could get 13 to 25 centimetres and up to 40 centimetres in spots, the U.S. National Hurricane Center said.

A National Guard official, John Anderson, said many people were complying with the evacuation orders.

"We have not seen much resistance at all."