Residents are running out of time to evacuate before Hurricane Florence roars in to North and South Carolina bringing potentially deadly flooding, officials warn.
South Carolina authorities have turned four motorways into one-way routes away from the coast to speed the exodus.
The category 4 storm carrying maximum sustained winds of 215 km/h would probably strike the southern coast of North Carolina by late Thursday or early Friday, the National Hurricane Center (NHC) said.
Forecasts showed the storm lingering near the coast of the Carolinas, carrying days of heavy rains that could bring intense inland flooding from South Carolina to Virginia. Parts of North Carolina could get 1m of rainfall.
Georgia Governor Nathan Deal, concerned the storm would bring its devastation south, issued an emergency declaration for all 159 counties in the state.
"Be prepared for the inland effects of the storm as well as the ensuing storm surge in coastal areas," Mr Deal said in a statement.
Jeff Byard of the Federal Emergency Management Agency (FEMA) invoked a former boxing champion to warn residents that it would bring "a Mike Tyson punch to the Carolina coast."
"Heed the warnings," Mr Byard said.
North Carolina Governor Roy Cooper warned that "disaster is at the doorstep", and "tens of thousands" of buildings may be flooded.
An NHC plane flying inside the storm found that pressure is continuing to drop, indicating its strength may still be growing.
Waves measuring 83ft (25m) tall were recorded at sea on Wednesday morning.
Nearly 1000 prisoners in South Carolina will not be moved from their cells, despite a mandatory evacuation order in the area. "In the past, it's been safer to leave them there," a state department of corrections spokesman said.
NHC Director Ken Graham warned that rivers up to 60km inland may flood.
Mr Graham said the Pamlico and Neuse rivers in North Carolina will see their flows "reversed" as storm surges push water back inland.
North Carolina farms are moving livestock to safety. In 1999, Hurricane Floyd left hundreds of thousands of dead hogs and chickens floating in floodwaters in the state.
- Reuters / BBC