Quite a few years ago I had to renew via Hong Kong, but I am aware that the system has changed. Taking at least 10 weeks to get a new passport apaprently.
It has been a while, but last time I did this, when I received the new passport in the post I just took old and new to the local Immigration where they filled in the first two pages of the new passport with details from the old. There were no documents from the embassy.