HONG KONG — Hong Kong has disqualified a 21-year-old democracy advocate from running for the local legislature, the latest in a series of young politicians to be barred from public office over their resistance to the Chinese government’s authority over the city.

The pro-democracy party Demosisto said on Saturday that election authorities had barred its candidate, Agnes Chow, from running in a March by-election, in which Hong Kong voters will decide on the members of the Legislative Council.

Ms. Chow said the ruling was “no less than a declaration to the city that our political rights are handicapped.”

In a statement Saturday, Hong Kong’s government said that a legislator “cannot possibly uphold” the city’s de facto constitution, the Basic Law — which says that Hong Kong is an inalienable part of China — if he or she “advocates or promotes self-determination or independence by any means.”