Do I need to apply for a transit visa prior to my journey?

Hello,

I am Polish citizen and I will be flying to Sydney through Beijing on one ticket, staying at the airport for few hours to wait for my connecting flight. On my way back, I will change planes at Shanghai - again, staying there just for few hours and the whole journey will be on one ticket. I am flying with Air China, which, I assume, can be counted as an international carrier and the flights will be international as well.