TWOV 24 hours

Khaled, you have to be very precise... From Hong Kong to Guangzhou there is a flight operated by Cathay Pacific. Also, if you are taking Saudia you have to point that your next destination is in Saudi Arabia from where you will proceed to Cairo.

OK, this is fine. Now, if your entire transit time in Guangzhou, counted from your scheduled arrival in Guangzhou, until your scheduled departure from Hong Kong, is shorter than 24 hours, you are perfectly covered by 24 hours visa free transit and you do not need any kind of visa.

Since you will fly on separate tickets and on unrelated airlines, you will approach, immediately upon landing to 24/144 hour visa free transit counter where you will apply for a temporary entry permit. This application is for free, but is essential because you will have to collect your luggage and perform new check-in for your Saudia flight to Cairo. In order to do that, you will be allowed to formally enter China and to perform all you have to do for your next flight. If you have longer layover, you can also visit Guangzhou and spend some time there exploring the city. However, have in mind that your layover cannot be longer than 24 hours even for just one minute!