Upvote:2
I have successfully applied for a new tourist visa while holding an old one. As it turned out the old visa had a few minutes left on it when we arrived, the passport official simply cancelled it at that point (entries didn't matter as these were multi-entry visas.)
While I have never had either a double-entry or a F visa I would expect things to work the same.
Upvote:3
I have also successfully applied for a new visa while the old one still there in Hong Kong. In Hong Kong is very easy to obtain Chinese visa. Just go to a travel agency, I paid around 150 HK dollars and I get a new visa in two days.