Orders for hundreds of miles of the US’s eastern seaboard to be evacuated have been issued as the joint strongest hurricane to ever make landfall has already caused extensive damage to the Bahamas.

One child has reportedly been killed on the Bahaman island of Abaco where floodwaters reaching 18-23 feet (5.5-7 metres) caused “catastrophic conditions”, inundating homes and while winds gusting up to 220 miles per hour tore buildings’ roofs off.

Hurricane Dorian – a category 5 storm with sustained winds of 185mph – is expected to continue slowly moving over Grand Bahama on Monday, before its path curves north-east, running parallel with the US coast.

Forecasters said they expect it to remain just off Florida and Georgia on Tuesday and Wednesday, hammering the coast with dangerous winds and heavy surf, before buffeting South Carolina and North Carolina on Thursday.

But there is still a chance it could make landfall and storm surges are forecast, prompting coastal evacuation orders in three states – South Carolina, Georgia and parts of Florida.

Tropical storm Dorian expected to strengthen to hurricane Show all 7 1 /7 Tropical storm Dorian expected to strengthen to hurricane Tropical storm Dorian expected to strengthen to hurricane Shoppers preparing for the arrival of tropical storm Dorian stock up on supplies at a supermarket in Bridgetown, Barbados, on 25 August 2019. The US National Hurricane Centre warned the storm was expected to strengthen to a hurricane by the time it reached Puerto Rico on 28 August 2019. REUTERS/Nigel R Browne Tropical storm Dorian expected to strengthen to hurricane Residents board up a pharmacy in Bridgetown, Barbados, 26 August 2019. AP/Chris Brandis Tropical storm Dorian expected to strengthen to hurricane Storm clouds gather as tropical storm Dorian moves towards St Michael Parish, Barbados, 26 August 2019. AP/Chris Brandis Tropical storm Dorian expected to strengthen to hurricane Nearly empty shelves where bottled water is normally displayed at a supermarket in Cabo Rojo, Puerto Rico, 26 August 2019. REUTERS/Ricardo Arduengo Tropical storm Dorian expected to strengthen to hurricane Hotel employees remove sun loungers from a pool area in Gros Islet, St Lucia, 26 August 2019. REUTERS/Andrea de Silva Tropical storm Dorian expected to strengthen to hurricane Empty shelves that are normally filled with bread are seen empty at a supermarket in Gros Islet, St Lucia, 26 August 2019. REUTERS/Andrea de Silva Tropical storm Dorian expected to strengthen to hurricane Tropical storm Dorian is pictured off the coast of Venezuela in this NASA satellite photo, 26 August 2019. NASA/Handout via Reuters

South Carolina Governor Henry McMaster ordered a mandatory evacuation of the entire coast of the state amid Dorian's threat. The order, which covers about 830,000 people, goes into effect at noon local time on Monday, when state troopers will begin reversing lanes so they all head inland on major coastal highways.

"We can't make everybody happy," Mr McMaster said. "But we believe we can keep everyone alive."

Georgia's governor Brian Kemp also ordered a mandatory evacuation of the state's Atlantic coast, also starting at noon on Monday.

Authorities in Florida ordered mandatory evacuations in some vulnerable coastal areas.

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The National Hurricane Centre issued a hurricane watch for Florida's east coast from Deerfield Beach north to the Volusia and Brevard county line. The same area was put under a storm surge watch. Lake Okeechobee was under a tropical storm watch.

Florida governor Ron DeSantis warned the state's densely populated Atlantic coast: “We're not out of the woods yet.”

He noted that some forecast models still bring Dorian close to or even onto the Florida peninsula.

“That could produce life-threatening storm surge and hurricane force winds,” he said.

“That cone of uncertainty still includes a lot of areas on the east coast of Florida and even into central and north Florida, so we are staying prepared and remaining vigilant.”

More than 600 flights in the US had been cancelled on Monday, which is Labour Day – a national holiday in America.

The only recorded storm that was more powerful was Hurricane Allen in 1980, with 190mph winds, but it did not make landfall at that strength.

Dorian has equalled a record set by a Labour Day storm from 1935. That storm, which occurred before hurricanes were given names, ultimately left major damage in its wake in the Florida Keys.

In the Bahamas on some parts of Abaco, the impact of Hurrican Dorian meant “you cannot tell the difference as to the beginning of the street versus where the ocean begins”, said Prime Minister Hubert Minnis.

According to the Nassau Guardian, he called it “probably the most sad and worst day of my life to address the Bahamian people”.

Earlier, Mr Minnis had warned that anyone who did not evacuate was “in extreme danger and can expect a catastrophic consequence”.

The government opened 14 shelters across the Bahamas. Dozens ignored evacuation orders, officials said.