Some helpful links:

Australian State and Territory authorities.

Immigration and citizenship for children adopted oversees.

Adopted children usually enter Australia on an Adoption (Subclass 102) Visa. A child must meet a number of requirements to be eligible for this visa.

The Australian Central Authority, ensures that adoptions adhere to the Hague Convention.
However, it does not deal with matters of immigration and citizenship.

The Department of Immigration and Citizenship is responsible for immigration, visas and citizenship in Australia. It assesses visas and Australian citizenship applications. For more information on immigration and citizenship requirements, including requirements for children adopted overseas visit the Department of Immigration and Citizenship website.

Information on adoption visas.

Information Australian citizenship.

Australian citizenship instructions for international adoption. (see page 19 and 30)

Intercountry adoption from China.

Countries not part of the Hague Convention that has an agreement with Australian authorities for adoptions: