Three people died in North Carolina, said Governor Pat McCrory, who called Matthew "a very, very serious" storm.
In Georgia, three people died, including a wheelchair user after two trees fell on his home. Five people were earlier killed in Florida.
Matthew has been the most powerful storm to make US landfall in more than a decade.
Thousands of people have been evacuated from their homes, and more than a million left without power.
The storm also brought heavy flooding to the historic city of Charleston, South Carolina.
Matthew has already caused nearly 900 deaths in Haiti and four in the Dominican Republic as it travelled northwards over the past few days.