12 month multi visit visa for US citizen living in Australia

Hello, we have a US citizen working in Australia on a 457 visa. He has previously had two 6 month 2 visit ones and now requires a 12 month multi visit one to China. We have all the required documentation necessary to apply for it.

Would you kindly advise whether he would have to apply for this in the United States or whether this can be done in Australia? If Australia, can you please advise which embassy we should apply to.

Please let me know if you require any additional information.