Rescuers have begun to reach areas of the northern Bahamas devastated by Hurricane Dorian.
Prime Minister Hubert Minnis said some areas had been "decimated" as the death toll rose to at least 20.
The hurricane winds that hit the Abaco Islands equalled the highest ever recorded at landfall, and Grand Bahama also suffered severe damage and floods.
Mr Minnis said the Bahamas was facing "one of the greatest national crises in our country's history".
Lia Head-Rigby, who runs a relief group and overflew the Abacos, said her representatives had told her there were "a lot more dead".
"It's total devastation. It's decimated. Apocalyptic," she told the Associated Press (AP) news agency.
Aerial images over the Abacos, including the port town of Marsh Harbour, showed mile upon mile of destruction, with roofs torn off, scattered debris, overturned cars, shipping containers and boats, and high water levels.
"There's nothing left in most of Marsh Harbour," said Alicia Cook, who evacuated from the area. "People are starting to panic: pillaging, looting... it's just no way everyone's going to get out."
Bob Cornea was evacuated from Marsh Harbour to the capital Nassau. He said he and his wife took shelter on the second storey of their son's house.
"Water was up to my neck. It stayed like that for two or three hours... My son... he got us out and we got over to safety.
"We've been through all kinds of hurricanes, all kinds of storms: never anything that bad. I mean, it was like we were standing in the middle of the ocean. That's what it looked like. Waves, the water just crashing in over us. Horrifying. Absolutely horrifying."
Parts of the Bahamas received up to 89cm of rain.
The situation on Grand Bahama is less clear, as Dorian only moved on late on Tuesday after nearly two days of pummelling, cutting many communication lines.
Most rescue work was being done on an ad hoc basis by locals using boats and jet skis, but it was being hampered by flooded roads, fallen trees and submerged debris.
Rescue teams were "beginning to get on the ground", National Security Minister Marvin Dames said on Wednesday, according to AP.
The International Red Cross fears 45 percent of homes on Grand Bahama and the Abacos - some 13,000 properties - have been severely damaged or destroyed.
Some 60,000 people will need food aid and clean water, UN officials say.
Dorian has moved off north and but still threatens the eastern US seaboard. Although the hurricane has weakened to a category two storm with maximum sustained winds of 165km/h, it has grown larger in area.
Forecasters have warned it could make landfall on the coast of South or North Carolina on Thursday.