Rear Admiral Eric Jones, who oversees U.S. Coast Guard operations in the Southeast U.S. and Caribbean, says officials are working "tirelessly" to get to hard-hit areas in the Bahamas. Many buildings that had not been flattened had walls or roofs partly ripped away.
Tropical-storm-force winds hampered the efforts, flipping over some of the jet skis.
Storm surges started to hit the Florida coast on Monday.
While Dorian's track is far from certain, it appears as though it will be several hundred miles off shore when it passes New Jersey with none of the state in the so-called "cone of uncertainty".
Dorian has wrecked thousands of homes and reportedly completely submerged the Bahama's Freeport Airport.
"We have not been able to assess the damages on Grand Bahama Island just yet".
"From all accounts we have received catastrophic damage". Virginia could feel the effects of the storm in the coming days. Some fear the death toll could rise.
Initial Red Cross estimates were that 13,000 buildings may have been damaged or destroyed by Dorian in the Bahamas, officials in Geneva said.
A text message seen by AFP from a woman named Kendra Williams, who lives on Grand Bahama, said: "We are under water; we are up in the ceiling".More news: Dolphins Trade LB Kiko Alonso To The Saints
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The airport in Grand Bahama was under two metres of water on Tuesday.
As Dorian tracks toward the US mainland, storm effects are likely to be felt along the southeastern coast from Florida up to North Carolina.
Forecasters have told Floridians not to become complacent.
Hurricane Dorian has caused more than 1,300 flights to be canceled within, as well as into and out of, the U.S.
Personnel from the 45th Space Wing of the U.S. Air Force, which is headquartered at nearby Cape Canaveral Air Force Station, are also on hand at NASA's Launch Control Center for the hurricane.
American Airlines said airport operations had been suspended at seven airports in Florida and the Bahamas, and a travel alert issued for more than 20 airports including in Georgia, North Carolina and SC. "You know, God always provides, y'all", Sammye Wooded said.
"South Carolina is still in the path of what is a very destructive and deadly storm", McMaster said.
"I came yesterday, as soon as it opened".
A mandatory evacuation of entire SC 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 Labor Day, Gov. Henry McMaster said.