# checkout repository A
git checkout git@github.com:username/repoA.git
# cd into old repository
cd repoA
# change remote origin to the newely created repo (exemple repoB)
git remote set-url origin git@github.com:username/repoB.git
# push branch into repoB
git push origin <branch>
# cd into new repository and pull branch
git checkout origin <branch>
# finally don't forget to reset origin for repoA
git remote set-url origin git@github.com:username/repoA.git
--First get original repo.
$ git clone --bare https://gitsite.com/yourusername/original-repository.git
$ cd original-repository
$ git push --mirror https://gitsite.com/yourusername/new-repository.git