Dual nationals who return to China with China passports.

China's laws absolutely forbid dual nationality.

You can go back to China with a China passport, that is, you will be regarded as a citizen of China after going through customs. However, you can't explain why you didn't have a valid Australian visa on your China passport when you crossed the border with China. In other words, you are regarded as an illegal returnee and will be fined.

And you can't go back to Australia with a China passport after entering the country, because you are an Australian citizen, so you can't apply for an Australian visa. You can't cross the border of China without an Australian visa.

Secondly, you can't leave the country with an Australian passport, because you don't have the corresponding entry record with this passport, which will be regarded as illegal residence or entering China through informal channels, which is illegal.

To sum up, Australian citizens with China passports can enter China, but the consequences will be unimaginable.