"Any attempt to mess up Hong Kong, or even damage its prosperity and stability, will not succeed," Mr. Wang told reporters after he met Japanese Prime Minister Shinzo Abe in Tokyo.
Hong Kong's pro-democracy camp was headed for a thumping victory in district council elections, local media reported on Monday, a vote widely seen as a referendum on the Beijing-backed government's handling of months of violent political unrest.
Counting was still under way following record turnout in Sunday's elections, but results so far indicated that candidates favoring calls for greater democracy were on course to seize a shock majority of the 452 seats contested, media reports said, AFP reported.
District councils - which handle community-level concerns such as bus routes and garbage collection - have long been dominated by the pro-Beijing establishment.
The pro-democracy camp hopes weakening that grip would send a message to China and Hong Kong's unpopular leader Carrie Lam.
Hong Kong has endured months of mass rallies and violent clashes pitting police against protesters who are mobilized by fears that Beijing is whittling away at the semi-autonomous territory's freedoms, which are unique for China.
Their demands include direct popular elections and a probe into alleged police brutality against demonstrators.