It is possible for UK citizen to apply for a Visa while in China?

I am potentially going to work for an animal charity organisation in South Africa for a minimum period of 2 years. I am aware that I need to obtain a 2-3 year volunteer V. I am a UK citizen but I am currently working in Chengdu, China. I am aware that it is better to apply for the V in your own country but that would entail flying back to the UK, applying for the V and then flying to South Africa. I would like to know if it would be possible to apply for it while still in China so that I can fly direct to South Africa from China once mine finishes, that way I can start my voluntary position as soon as possible. If it is possible, I would also like to know if I could send my application through the post (much like in the UK) and how long it takes to process. I look forward to hearing from you. Thank you for your time.