Monster storm Dorian unleashed "catastrophic conditions" as it hit the northwestern Bahamas Sunday, becoming the strongest hurricane ever recorded in the region, US forecasters said.

"Catastrophic hurricane conditions are occurring in the Abacos Islands and will spread across Grand Bahama Island later today and tonight," the National Hurricane Center wrote in its latest bulletin at 3pm (GMT).

Packing maximum sustained winds of 180 miles per hour (285 kph), the NHC said Dorian was now "the strongest hurricane in modern records for the northwestern Bahamas."

Dorian's eye has reached 20 miles from the Abaco islands, and the hurricane's core was expected to move directly over Great Abaco, and possibly Grand Bahama Island later Sunday and Monday, the NHC said.

It would then head for Miami but it was unclear if it would skim the coast and head North, or move inland.