Hurricane Nicole has ploughed through the Bahamas, lashing the West Indies island nation with howling winds and raging surf while churning closer to Florida's Atlantic shoreline.
Nicole was packing sustained winds of up 120km/h as it made landfall on Grand Bahama Island, and was expected to move ashore over the eastern seaboard of Florida late on Wednesday or early Thursday, the Miami-based National Hurricane Centre reported.
Authorities in several counties along Florida's east coast issued mandatory evacuation orders or advised residents in low-lying areas along the shore and on barrier islands to seek shelter.
"This is the last window of opportunity to secure your families and to secure your properties and possibly save some lives," Volusia County Sheriff Mike Chitwood said in a video posted online, urging residents to heed evacuation orders.
Chitwood said "dozens upon dozens" of oceanside buildings, including high-rise condominiums, were left structurally unsafe in Volusia County after Florida's last major storm, Hurricane Ian, struck six weeks ago, with some now "in imminent danger of collapsing" when Nicole strikes.
Video footage posted on social media showed ocean waves crashing up onto streets and parking areas under foreboding skies.
Even before reaching hurricane strength, the storm unleashed "extensive flooding" across much of the Bahamas, including the islands of Grand Bahama, Eleuthera, Andros and the Abacos, National Emergency Management Agency chief Captain Stephen Russell told a news conference.
Grand Bahama, Bimini and the Berry Islands in the northwest corner of the island nation remained under a hurricane warning.
As the storm closed in earlier on Wednesday, some residents fled their homes amid fierce winds and flooding.
Ann Wilmore, 60, of Dundas Town on the island of Abaco, left her trailer and sought refuge in a nearby house. "I'm monitoring the weather very closely," Wilmore said by telephone.
The Bahamas Department of Meteorology reported a nearly 1.2 metre storm surge north of the town of Treasure Cay on Abaco. Waves flooded at least one road in Nassau, the capital, officials said.
The storm's centre was expected to pass well north of Miami, Florida's most populous city.
But Governor Ron DeSantis declared a state of emergency for 45 counties, and a hurricane warning remain posted for Florida's Atlantic seaboard from Boca Raton north to around Flagler Beach.
The National Hurricane Centre also issued storm-surge advisories for much of Florida's east coast, warning that wind-driven waves were expected to wash over beaches and rush inland to flood low-lying areas well beyond the shore.
Storm surges caused widespread devastation to Florida's Gulf Coast when Hurricane Ian crashed ashore on September 28, causing an estimated $US60 billion ($A93 billion) in damage and killing more than 140 people.
DeSantis urged residents to prepare.
"Please make a plan," he told a news conference. "This is likely to be a storm making landfall and will affect huge parts of Florida."
State officials opened 15 emergency shelters across the region, activated 600 National Guard troops for emergency response and recovery efforts, and placed 1600 utility workers on standby to restore power knocked out by the storm.
More than a dozen school districts were closed on Wednesday and more than 20 school districts across the state were scheduled to be closed on Thursday.
Orlando International Airport announced it was ceasing commercial operations at 4pm on Wednesday.
The storm was expected to move into southern Georgia on Thursday before moving into the Carolinas on Friday.