Mystery over how mainland celebrity was allowed to give birth in Hong Kong

News that a mainland celebrity couple delivered their second child in Hong Kong at the weekend has raised speculation that a loophole exists in a ban on mainlanders giving birth in the city.

Mainland internet users were left scratching their heads after actress Betty Sun Li on Saturday night announced on Weibo - the mainland's equivalent of Twitter - that she had delivered a daughter in Hong Kong.

"Deng Deng's sister has arrived," Sun wrote on her microblog, referring to her young son.

The agent of actor Deng Chao, Sun's husband, confirmed the news but refused to reveal the hospital where she had given birth or whether either of the parents had obtained Hong Kong permanent residency.

The posting prompted the mainland online community to speculate how the couple could have given birth in Hong Kong legally, given its "zero birth quota" policy, in place since last year.

The rule stops pregnant mainlanders from taking up resources at local hospitals, and skirts the issue of granting residency rights to babies born in Hong Kong to mainland parents.