Authorities in the Bahamas made a last-minute plea to residents and tourists on Saturday to seek shelter as time ran out before powerful Hurricane Dorian hits, warning those that refused to move that their lives were at risk.

"Hurricane Dorian is a devastating, dangerous storm approaching our islands," Bahamas Prime Minister Hubert Minnis said in a nationally televised news conference.

Packing maximum sustained winds of 240 km/h, the Category 4 storm was forecast to hit the Bahamas on Sunday with more than 60 centimetres of rainfall in places, the U.S. National Hurricane Center said.

Dorian was later due to threaten Georgia and the Carolinas, possibly sparing Florida a direct hit, as communities in those states raised alert levels.

In its direct, immediate path, the monster storm was headed for the Bahamian northwestern islands of Grand Bahama and Abaco.

Minnis said that 73,000 people and 21,000 homes were at risk to storm surges of up to 4.6 meters.

"Dorian will now create prolonged periods of large swells, surges along the north coast of Grand Bahama and the north and east coast of Abaco," said Jeffery Simmons, the deputy director of Bahamas' department of meteorology.

Local residents fill sandbags to protect their homes ahead of the arrival of Hurricane Dorian in Kissimmee, Fla., on Friday. (Gregg Newton/Reuters)

"We are asking residents in those areas to leave the coastline, we expect a storm surge of up to 15 feet, in addition to that we have a spring tide that can increase the surge by two to three feet," Simmons added.

Once the storm unleashes its fury on the archipelago nation, people will have to ride out Dorian before first responders can venture outside to rescue anyone.

<a href="https://twitter.com/hashtag/Dorian?src=hash&ref_src=twsrc%5Etfw">#Dorian</a> is a powerful category 4 hurricane. Here are the Key Messages from the 5 pm EDT advisory. <a href="https://t.co/jHCuANBNSQ">pic.twitter.com/jHCuANBNSQ</a> —@NHC_Atlantic

Rescue workers will not be able to move with winds up to 240 km/h, so those individuals that want to are advised to do so now, said Minnis.

Grand Bahama and Abaco are hubs for the Bahamas' thriving tourism industry. The nation owes nearly 30 per cent of its direct gross domestic product and half of its jobs to the industry, said Joy Jibrilu, director general of the Ministry of Tourism.

The country is still reeling from Hurricane Matthew, which ripped into the Bahamas in 2016, as some hotels have taken years to make repairs.

In 2017, the Bahamas tourism industry sagged when Hurricanes Irma and Maria cut a deadly path across the Caribbean, though they largely spared the archipelago. The World Travel and Tourism Council said the two storms caused an estimated drop of 826,100 visitors across the region.

"I want you to remember: homes, houses, structures can be replaced. Lives cannot be replaced," Minnis warned.

The storm-prone Bahamas, on average, faces a direct hit from a hurricane every four years, officials say.

Construction codes require homes to have metal reinforcements for roof beams to withstand winds into the upper limits of a Category 4 hurricane, and compliance is generally tight for residents who can afford it. Poorer communities typically have wooden homes and are generally lower-lying, placing them at tremendous risk.

Hurricane now forecast to skim U.S. coast

After walloping the islands, forecasters said the ever-strengthening Dorian was expected to dance up the southeast U.S. coastline, staying just off the shores of Florida and Georgia on Tuesday and Wednesday before skirting South Carolina and North Carolina on Thursday.

South Carolina Gov. Henry McMaster declared a state of emergency Saturday, mobilizing state resources to prepare for the possibility the storm could still make landfall. Trump already declared a state of emergency in Florida and authorized the Federal Emergency Management Agency (FEMA) to co-ordinate disaster-relief efforts.

The National Hurricane Center in Miami said the risk of strong winds and rising water will increase along the shores of Georgia and the Carolinas by midweek.

The centre also stressed that Dorian could still hit Florida, where millions of people have been in the storm's changing potential path. But after days of a forecast that put the state in the centre of expected landfalls, the hurricane's turn northeast is significant.

Carmen Segura, 32, said she had installed hurricane shutters at her house in Miami, bought extra gas and secured water and food for at least three days. She feels well prepared and less worried given the latest forecasts but still a bit uneasy given how unpredictable the storm's expected track has been.

"Part of me still feels like: So now what?" Segura said.

Florida Gov. Ron DeSantis warned people not to let their guard down.

"Looking at these forecasts, a bump in one direction or the other could have really significant ramifications in terms of impact," DeSantis said. "If it bumps further east, that obviously is positive. If it bumps just a little west, then you're looking at really, really significant impacts."

Storm hovers over long weekend

The storm upended some Labour Day weekend plans: Major airlines allowed travellers to change their reservations without fees, big cruise lines began rerouting their ships and Cumberland Island National Seashore, off Georgia's coast, closed to visitors.

Disney World and Orlando's other resorts could be at risk, but they held off announcing any closings, with Dorian days away and its track uncertain.

In this NOAA satellite image taken on Aug. 31, 2019, Hurricane Dorian tracks toward the Florida coast in the Atlantic Ocean. A hurricane warning is in effect for the northwestern Bahamas, where Dorian will arrive Sunday. (NOAA via Getty Images)

Sherry Atkinson, who manages a hotel on North Carolina's Outer Banks, said the hurricane wasn't spoiling holiday vacations for guests.

"Everybody is just kind of chilly-willy. They know it's not going to bother their weekend," she said.

Atkinson said she has lived on the Outer Banks for 26 years and that, so far, "there hasn't even been a snippet of conversation about evacuations."

Florida authorities have not ordered mass evacuations but some counties told residents of barrier islands, mobile homes and low-lying areas to flee beginning Sunday — though those orders could change.

Dorian was centred 625 kilometres east of West Palm Beach and was moving west at 13 km/h.