US President Barack Obama has declared a state of emergency in Florida and South Carolina as Hurricane Matthew continues its devastating path from the Caribbean northwards.
The storm is one of the biggest to hit the area in the last ten years, and has so far killed at least 339 people, mostly in Haiti.
There are mass evacuations in four US states: Florida, Georgia and North and South Carolina.
Highways leading inland from Florida's eastern coastline are packed with traffic fleeing Hurricane Matthew.
Authorities are worried about those who are refusing to evacuate, with the mega-storm just hours away from making landfall.
South Carolina Governor Nikki Haley held a press conference at 6pm on Thursday (11am Friday, NZ Time).
"As of 3pm today, we had 280,000 who have evacuated, up from 175,000 this morning. We hope to see stronger numbers," she said.
Some residents were offering free shelter for evacuees, she said. The storm is so severe that the hospital in the coastal city of Beaufort has been evacuated.
"This is really a serious storm. I am begging you to understand the seriousness of the storm," Haley said.
The storm surge produced by Hurricane Matthew is expected to reach more two to three metres along the Florida coast and is considered life threatening, Ed Rappaport, deputy director of the National Hurricane Center, told CNN.
"What we know is that most of the lives lost in hurricanes is due to storm surge," he said.
The storm is "closing in on the coast" with winds extending 80 miles out from its centre.
Forecasters however don't expect it to strengthen beyond Category 4. It's unclear if the hurricane would make landfall in Florida or skirt along the coast, Mr Rappaport said.
Miami-Dade County mayor Carlos Gimenez said at a press conference that he expected the worst of the storm to have passed the area by midnight.
Reuters / Newshub.