Round Trip to Shanghai, but leaving to a third country between flight

There are no problems at all. You can use in both cases visa free transit options. I would assume that at the first leg, you will stay just for a limited amount of time (just a few hours) in Shanghai, so it would be 24 hours TWOV and in the second case 144 hours free transit.

You first leg will be Tijuana (Mexico) - Shanghai (China) - Hong Kong (fine because considered as a third country for visa free travel purposes).

Your second leg will be Manila (Philippines) - Shanghai (China) - Ciudad de México City (Mexico). Everything according to the book.

In fact, my flight to Shanghai arrives at 9:30am of April 28th and I leave Shanghai to HK next day at 9:15am. But HK counts as third country, right? So it will be 24h visa. My only concern was if I could get two free visa transit since I booked a round trip. The consulate in Brazil told me they couldn't guarantee I could get it on my way back, but they usually issue it with no problems.

And thank you for your info!!

You are just fine for both legs of your trip. In the first case, you will be covered by 24 hours TWOV and here you should have in mind to have your accommodation book in advance and with a printed confirmation in your hands along with your ticket for your onward flight, so that you obtain entry permit. By the way, I confirm that Hong Kong is fine as it counts as a third country regarding all the options of visa free travel in mainland China

In the second case, you will apply for 144 hours visa free transit. Again, printed confirmation of your accommodation booking and your onward ticket for your home country or to any other country different that Philippines and not a single landing more within the mainland China.

You as a Brazilian (or Mexican) citizen will be allowed to obtain all the mentioned visa free transits. You should not worry about, but just follow the suggestions and you will be fine.

Thank you once again! Your info has been really helpful!
Just two more questions: I read I have to informe the airline that I'll be applying for the free visa transit during my check in so they will inform the immigration office in Shanghai in advance. I called them and they seem not to be aware of this process. In case they fail in informing the immigration office before I apply for the free visa transit, will I be in any trouble?
Besides, I booked to different places during my 3 nights staying when I arrive from the Philippines. Is that ok? I should just show both booking confirmations to the immigration officer, right?

Actually, you should inform your company that you are traveling through China using 144 hours visa free transit and not "free visa transit". This is very important because visa free means that you will not receive any kind of visa and free visa means that you will receive some kind of free visa. So, these are very different things. To inform your company in the best way possible, you should just make them to use Timatic, a comprehensive guide for all the airline companies and immigration authorities where the situation of visa free transit through China is explained in its purest form and leaves nobody with any additional question. So, you will be just fine, especially because you will board in Mexico City on a flight that flies directly (although with a stop in Tijuana) to Shanghai. It is perfectly normal that the check-in staff and other relevant authorities will consult Timatic in case that they are not so familiar with this process. Anyway, I'm more than positive that they had and will have several more passengers beside you using this convenience for their flights via China.

It is perfectly OK for Chinese immigration to see that an applicant has booked two different accommodations during her/his stay in Shanghai or wherever. You should just have printed accommodation confirmations (along with your flight tickets, of course) and everything will be just fine.

Thank you very much!! It's been really stressful to find realible information and I was really scared with the perspective of not being allowed to follow my trip. Much more releaved now!
I think someone has already asked that, but the airlines of my two routes (MEX-Shanghai is AeroMexico and Shanghai-HK is HK Airlines) dont have any kind of relationship. Same thing with the airline from Philippines (Cebu). I figured it wouldn't be a problem since they allow you to enter by air and leave by train, which do not have any kind of relationship between them. Is that right?

I'm asking that because since they are different airlines, I won't have my boarding pass with me, just my flight booking confirmation. I guess it's enough, right?

True. There is no any problem regarding the fact of use of different airlines and separate tickets. The largest majority of visitors to Shanghai on 144 hours visa free transit don't have boarding passes, but just a flight confirmation. By the way, keep in mind to have at hand a flight confirmation with that long flight number (in reality a kind of code) that you will write it on your application for 144 hours visa free transit. To conclude, the non-existent relationship between the airlines is insignificant.

I can't thank you enough for your help! I'm more confident now that everything is gonna work well :)

I have a doubt: since I bought a round trip MEX-SHA/SHA-MEX (same reservation), technically if I miss the first leg (which I dont intend to), the airline will cancel my return flight (SHA-MEX). I suppose the immigration office can check if my onward flight is confirmed with no problem, with the ticket number I provide, right? Also, the fact that all my flights SP-MEX-SHA/SHA-MEX-SP are all in the same ticket and all have the same ticket number is not gonna be an issue? I asked the airline if they could send me my flights in separate tickets, even if the number is the same, but they told me since it's only one reservation, they can't do it.

Thayna, there is no problem at all. As far as I have understood you, you will be traveling from Shanghai to Hong Kong, then Vietnam and then Philippines. After that you will return to Shanghai and proceed back to Mexico. So, there is no problem since you will exit China between the two legs of your return flight. Everything that interests Chinese authorities is this:

Leg 1: Mexico - Shanghai - Hong Kong.
Leg 2 : Philippines - Shanghai - Mexico.

Whether you have or not a return ticket Mexico - Shanghai - Mexico simply does not interest them.

To conclude, you can travel and enjoy your time in all the mentioned countries with peace of mind :).

P.S. Please, don't miss the first leg :)))...

Yes, that´s exactly my itinerary! Thank you very much, you´ve been really helpful! And for sure I wont miss my first leg :)
As far as I can see, my biggest issue will be convincing AeroMexico that I'm good to travel without a visa, but hopefully they are already used to it or there will be more people in the same situation.
Thank you once again!