HONG KONG—Government officials plan to propose a law that would make disrespecting China’s national anthem a crime, raising concern within opposition ranks that it would further narrow freedoms in the semiautonomous Chinese city.

The bill, which will be introduced in the city’s pro-Beijing legislature Jan. 23 for passage by the summer, is modeled on a similar law in mainland China. Aside from providing guidance on etiquette when the national anthem is played, it also stipulates that primary and high school children—including...