There are two distinct parts to this question.
The first part is (so to speak) "getting out of China".
The second part is (so to speak) "getting into Australia".
As to the first part:
If the marriage took place in China (and is valid according to Chinese Law); and
if the child is a PRC citizen by birth;* and
one parent does not consent to the removal, then any move to expatriate the child
will be a matter first for the equivalent of "family law" in China.
Questions of custody, consent to removal, and any arrangements for financial support and/or future visiting,
as well as permission to emigrate from China, will be dealt with according to the law of China.
Consider, for example, that it may be a requirement of the law in China that an emigrating national
departs on a PRC passport.
I am not in a position to advise on the specifics of family law in PRC.
Do consider however, that attempting to remove a PRC citizen (ie the child),
without the correct approvals and travel documents, may well be an offence (that is, a crime)
in PRC.
As to the second part:
It is possible that the child, even if born in mainland PRC, has acquired Australian
citizenship by descent
from its Australian citizen mother.
If so, then the child may be eligible to apply for an Australian passport.
It is necessary to obtain Australian citizenship before applying for an Australian passport.
Applications of this type can be made from
overseas.
Note that the process of issuing a passport does become more complex
when one parent does not consent.
It will be necessary to obtain the Australian passport before arriving in Australia.
A citizen-parent cannot just arrive in Australia with a baby in tow,
that may be a citizen of another country, but can't be shown to be an Australian citizen.
If that happens, then there is a very real risk that the child will be literally
taken from its parent's arms and placed in Immigration Detention
(that is, the baby can be gaoled, without its parent),**
until identity and ultimate nationality of the child can be determined.
I would strongly suggest that a mother in this kind of situation engage
a lawyer who is also a Migration Agent, to assist her with a matter of this complexity.
Please pay particular attention to my "signature" below.
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* As well as an Australian Citizen by descent (read on)
** If readers think that I feel strongly about this question,
they would be correct
