Residual powers are the power in a federal system of government not explicity laid down in a constitution.
Political scientist Ma Ngok said generally states in a federal system, through a written constitution, would hand over specific powers to the federal government.
Those not spelled out in the constitution are regarded as residual powers of the states and therefore within their own autonomy, he said.
In a speech on the Basic Law interpretation in 2004, Qiao Xiaoyang, deputy secretary-general of the National People's Congress Standing Committee, made clear that China is a unitary government system and therefore the concept of residual powers was not applicable.
He said the provincial authorities had no power of their own and all the powers were delegated by the central government.
Professor Ma said the residual powers concept had been thoroughly discussed during the Basic Law drafting process in the 1980s. Despite suggestions that Hong Kong only enjoyed what had been stated in the Basic Law, Professor Ma said people could still argue otherwise under the common-law principle.