HONG KONG—With his strategy to impose sweeping antisedition laws on Hong Kong, Chinese chief Xi Jinping has revealed a willingness to alter the onetime British colony’s unique standing as a self-governing town with a velocity and scope that has surprised lots of, from pro-democracy activists to diplomats to businesspeople.

At a meeting of mainland China’s Countrywide People’s Congress past week, authorities mentioned they would go all over Hong Kong’s possess legislature and draft steps in opposition to secession, international affect and terrorism…