The case of Australia's longest-serving detainee shows no signs of being resolved, the immigration ombudsman has found.

The woman, referred to in public documents as Ms X, has been in detention for more than nine years.

In October 2009, the United Nations Human Rights Committee (UNHRC) found her extended period of detention, without any substantive judicial review, was arbitrary.

On that basis, it concluded Australia had breached the International Covenant on Civil and Political Rights.

The UNHRC also warned that if Ms X was deported - without China promising not to harm her - Australia risked another breach of its international obligations.