Residents of the northern Bahamas, some trapped on the roofs of homes, have sent out pleas for help after Hurricane Dorian stalled over the area.
Dorian fell in strength on Tuesday to category three, but Grand Bahama island faced at least another day of heavy rain, high winds and storm surges.
The storm killed at least five people when it hit the Abaco Islands at category five with 185mph winds.
The eastern US coast remains on alert for Dorian to move in that direction.
The most recent update from the US National Hurricane Centre (NHC) placed Dorian just north of Grand Bahama, home to about 50,000 people, having moved barely 20km (12 miles) in a day.
The NHC described Dorian as “stationary” with maximum sustained winds of 120mph (195km/h, marking it as a category three on the Saffir-Simpson hurricane scale.
But the NHC warned that the storm was still producing higher gusts and storm surges 10ft-15ft (3m to 4.5m) above normal, and the agency advised residents to remain in shelter on Grand Bahama throughout Tuesday.
The winds at the core of the storm were spinning so fast that the centre of the storm was collapsing on itself, causing it to expand and damage a larger area, according to the BBC Weather service.
Steve McAndrew, of the International Red Cross, told the BBC he had been involved in rescue operations for 20 years and could not recall a hurricane ever being listed as stationary.
Palm Beach county in Florida – less than 100 miles to the west – saw gusts of up to 60mph on Tuesday.
Eyewitness videos and reports painted a picture of massive and widespread flooding, with panicked families fleeing to their roofs to escape rising floodwaters.
The Bahamas Press showed video of the Rand Memorial Hospital in Freeport under water, with patients forced to evacuate. The news site also relayed calls for help from residents trapped on roofs for hours.
Freeport resident Yasmin Rigby told the Reuters agency: “People who thought they were safe are now calling for help”.
Grand Bahama’s international airport was under 6ft of water, while residents posting on Twitter said a church in Freeport had lost its roof and scores of people were in danger.
Another Twitter posting called for the rescue of an aunt and nine others from rising waters in the town.
Journalist Kyle Walkine tweeted that he was in a three-storey building “believed to be one of the strongest in Freeport, and it is shaking. But Dorian doesn’t want to move”.
Clint Watson, a journalist based in the capital Nassau, said people in Grand Bahama were being hit with “buckets of rain” and posting videos online showing water rising to the windows of their attics.
“You can’t fathom that but that’s what people are showing us with their videos,” he told the BBC. “And you can see the water outside pressing in. It’s stories like that and images like that that you can’t get out of your mind.”
One radio station told the Associated Press news agency it had received more than 2,000 distress messages.
The picture was clearer on the Abaco Islands after Dorian moved further west. The islands, with a population of about 17,000, bore the brunt of the storm. No hurricane had ever made landfall with greater wind speeds. Only the 1935 Labor Day hurricane can match Dorian’s 185mph.
In addition to the five killed there, another 21 injured were airlifted to the capital Nassau by the US Coast Guard.
Prime Minister Hubert Minnis said on Monday that reports from the Abaco Islands suggested the devastation was “unprecedented”, calling the hurricane a “historic tragedy”.
Rescue operations were reportedly underway in areas it was safe to enter.