Biddulph - from the University of Melbourne and co-founder of the China Law Network - said Xu's detention should be seen in the context of refusals by the Ministry of Justice to re-register a number of activist lawyers and law firms at which they worked.

"I think most people who are looking at this issue are very concerned that it shows an increased wariness by the authorities about rights activist lawyers because they are the people who support petitioners, people who have grievances against the state in respect of a range of decisions and it's traditionally been quite difficult for those people to get legal representation," she said.

"These lawyers are orientated towards protecting rights and have been willing to take on those really difficult cases. It is of concern that in the last few months a number of these lawyers have been deregistered."

Around China, 53 lawyers who are involved in human rights work have had their licences suspended or rescinded, with legal aid group Yirenping Center raided on allegations of engaging in "unlicensed publishing activities", reported The Australian.

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Those who have not been able to renew their annual registration can't practise as lawyers, said Biddulph.

"It is a setback for those whose main focus is on 'rights protection cases'. This might also act as a disincentive to other people considering taking on this type of case," she said

- Sarah Sharples