Is it necessary to fly with the same airline with a layover in China to get a visa-free transit?

No, it is not necessary. The rules of visa-free transit through China have no restrictions on this matter, i.e., you can freely fly with a layover with any airlines. The only difference when flying with different airlines is that in such a case, during a layover at some airports in China, you will have to apply for visa-free transit, go through passport and customs control, check in for the next flight with the other airline, and then go through all controls again. Therefore, for such a layover, it is better to allow at least 5 hours to minimize the risk of missing the next flight. More details about transit rules in China here - https://nashaplaneta.net/besopasnost/novye-pravila-tranzita-cherez-kitaj-10-dnej-bez-vizy

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