'We can't tell what they are now as time is needed for a problem to emerge.' The post-handover government needed to issue a more detailed set of guidelines, Mr Wu said.

It is understood Chinese officials will explain details of the document to government officials at an experts' meeting in the Joint Liaison Group this month.

According to Xinhua (the New China News Agency), the document was passed by the Standing Committee of the National People's Congress (NPC) by 129-1.

Xinhua did not name the lone opponent or publish the whole document.

All ethnic Chinese citizens of Hong Kong who were born in either Hong Kong or China would be considered Chinese citizens after July 1, 1997, it said.

Holders of British National Overseas or British Dependent Territory Citizens passports or a passport granted under the British Nationality Select Scheme would still be deemed Chinese nationals.

But the document allowed for Chinese with foreign passports to apply to renounce their Chinese nationality through the Immigration Department.

Xinhua's local director Zhou Nan , who is also a member of the NPC's Standing Committee, said the issue needed to be resolved urgently because other decisions, such as the issuing of SAR passports and the selection of the chief executive and principal officials, hinged on it.

Preparatory Committee member Maria Tam Wai-chu urged Chinese nationals, who had migrated to a country which did not allow dual nationality, to make a declaration of their nationality.

This included the holders of passports of some Southeast Asian countries.

Ms Tam said the legislation would benefit Hong Kong people, making it convenient for them to carry out business.

Another committee member, Tam Yiu-chung, said the advantage of the system was that people holding foreign passports would be allowed to decide which nationality they wanted to claim.