Hurricane Matthew first made landfall in in the US in South Carolina but its edges had previously battered the coasts of Florida and Georgia.
The World Meteorological Organisation (WMO), which is the UN's weather agency, had warned that the hurricane would remain dangerous regardless of whether or not it made landfall in the US.
Parts of the city of Savannah, Georgia have been submerged in several feet (one foot = 30cm) of water.
Hurricane Matthew left up to 90% of some parts of Haiti destroyed, officials say.