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. Four 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.