A simulation weather video is showing what the life-threatening Hurricane Florence storm surge might look like if it reaches a frightening nine feet.

Life-threatening storm surges of up to 11 feet have been forecast in some areas when the monster storm eventually makes landfall in North and South Carolina.

The Weather Channel's forecast video shows the potential damage such surges could inflict on the southern states.

The Weather Channel's forecast video shows the potential damage storm surges caused by Hurricane Florence could inflict on North and South Carolina

Dr Greg Postel, the network's hurricane specialist, said three feet of water was enough to knock people off their feet, potentially carry cars away and flood lower levels of buildings.

Six feet of storm surge could carry large objects like cars underwater and leave lower levels structures submerged in water, according to Dr Postel.

The video also gives a frightening indication of what nine feet of water looks like - completely submerging lower buildings.

In addition to the life-threatening storm surge, Florence is also forecast to dump up to 40 inches of rain after it makes landfall in North and South Carolina Thursday night or Friday.

THREE FEET: Three feet of storm surge is enough to knock people off their feet, potentially carry cars away and flood lower levels of buildings

SIX FEET: Storm surge of six feet could carry large objects like cars underwater and leave lower levels structures submerged in water

Florence's winds had dropped from a peak of 140 mph to 90 mph by late Thursday, reducing the hurricane from a terrifying Category 4 to a 1.

But forecasters warned that the widening storm - and its likelihood of lingering around the coast for days - will bring life-threatening storm surge and torrential rains.

The center of Florence is expected to hit North Carolina's southern coast Friday, then drift southwest before moving inland on Saturday.

Georgia joined North and South Carolina, Virginia and Maryland in issuing an emergency declaration as forecasts showed Florence dumping historic amounts of rain - potentially 10 trillion gallons - on the southern states.

The storm was already generating 83-foot waves at sea on Wednesday.

Forecasters at the National Hurricane Center warned that Florence remained deadly because of its size and slow forward speed, even if its top sustained winds have dropped it to Category 1 status as a hurricane.