An unauthorized addition to a luxury house may be sinking the hopes of the man thought to be China's favorite to be Hong Kong's next leader.

Henry Tang, a former senior government official, is facing increasing pressure to end his campaign to become chief executive, Hong Kong's top government position.

Long seen as the candidate favored by Beijing, Mr. Tang has seen his popularity plummet over months of missteps, capped last week when he acknowledged that structures built at his wife's home did not have government approval. Mr. Tang insists on continuing his candidacy, but the unauthorized construction, a favorite topic in local media coverage of public figures, was seized on by his political opponents.

"I don't think he can hope to salvage his credibility," said Alan Leong of the Civic Party. "If he can't handle his own affairs, how can he run a government?"