I have a flight from Guangzhou to Saudi Arabia, so can I buy a flight from HK to Guangzhou?

I am an Egyptian national. I have a flight leaving from Guangzhou to Saudi Arabia. I had a Chinese residence permit which is now expired. I am currently in Hong Kong. Can I book a flight from Hong Kong to Guangzhou on the same day as my departure to Saudi so my transit time will be less than 24 hours. Do I need a transit visa? If so can I apply for this in Hong Kong as I am unable to apply for any tourist or business type here, is applying for a transit G okay if I am not a resident of Hong Kong?