Officials in the Bahamas reported a “tremendous” number of calls from people in flooded homes, AP reported, with one radio station receiving more than 2000 distress messages.
One call involved a 5-month-old baby stranded on a roof and a grandmother with six grandchildren who cut a hole in a roof to escape rising floodwaters.
A group of eight children and five adults were reported stranded on a highway and two storm shelters that flooded.
Forecasters warned that Dorian could generate a storm surge as high as seven metres.
Police Chief Samuel Butler urged people to remain calm and share their GPS coordinates, but he said rescue crews had to wait until weather conditions improved.
“We simply cannot get to you,” he told Bahamas radio station ZNS.
On nearby Abaco Island, Parliament member Darren Henfield said he received reports of deaths but officials had not been able to confirm them.
Dorian has been downgraded from a category five to category four storm but the US National Hurricane Centre warned that it remained “extremely dangerous” for residents in Florida, Georgia and South Carolina.
“Winds have decreased to 165MPH but Dorian remains an extremely dangerous storm,” Bahamas PM Minnis said in a post on Twitter. “Our focus right now is rescue, recovery and prayer.”
An 8-year-old boy drowned during the hurricane, according to reports by two local news outlets.
Foreign Minister Darren Henfield told Bahamian broadcaster ZNS: “From all accounts, we have received catastrophic damage.”
“We have reports of casualties; we have reports of bodies being seen.”
Minister for Agriculture Michael Pintard posted a video on social media showing waves crashing against the windows of his home.
Mandatory evacuation orders have been issued for coastal communities in Florida ahead of the expected arrival of the hurricane on Monday night or Tuesday morning, local time.
Florida officials are worried locals are experiencing “hurricane fatigue” and may fail to make necessary preparations as the storm slowly approaches their state.
US President Donald Trump spent the day golfing at his resort in Virginia and did not comment about the hurricanes on Twitter.
The President spoke to Florida Governor Ron DeSantis, who said the President was “fully engaged” with federal, state and local officials.
Meteorologists and state officials corrected Trump on Sunday when he incorrectly said that Alabama could be affected by the hurricane.
Palm Beach International Airport and Fort Lauderdale-Hollywood International Airport shut down on Monday, local time, and will not re-open until the hurricane passes.
The National Hurricane Centre’s latest models predict that the hurricane will narrowly miss the US mainland, but forecasters warn that even a slight deviation could inflict massive destruction on the coastline.
“On this track, the core of extremely dangerous Hurricane Dorian will continue to pound Grand Bahama Island through much of today and tonight,” the centre said in an advisory issued on Monday, local time.
“The hurricane will then move dangerously close to the Florida east coast late tonight through Wednesday evening and then move dangerously close to the Georgia and South Carolina coasts on Wednesday night and Thursday.
“Although gradual weakening is forecast, Dorian is expected to remain a powerful hurricane during the next couple of days.”
Officials in South Carolina and Georgia have grown increasingly concerned about the storm’s path towards their states.
Matthew Knott a reporter for The Sydney Morning Herald and The Age based in the United States.