who are considered Chinese citizens by China.

That number would be very small according to Chinese Nationality Law:

"Chinese nationality law states that a person born abroad is a Chinese national through jus sanguinis if:

The person is born outside China with at least one parent who has Chinese nationality, and the parent (or parents) with Chinese nationality has not yet settled in a foreign country (Article 5), or

The person is not eligible for the nationality or citizenship of the birth country, regardless of the parents' immigration status in that country (e.g. Japan).

The term "settled" is usually taken to mean that the Chinese national parent has permanent residency in another country."

For those born in China and have taken Australia citizenship would de jure lose Chinese nationality.

"Chinese nationality is automatically lost (or terminated) when a person has settled abroad and pursues one of the following acts (Article 9):

naturalizes as a citizen of another country (regardless of whether the naturalization is involuntary), or

voluntarily acquires the nationality (through naturalization or registration) of another country."

The number would be far from a million unless you're speaking figuratively?