The trumpet sounds, clear and exultant, and is greeted by a crescendo of boos.

This was the scene at repeated Hong Kong football matches, as fans in the semi-autonomous Chinese city expressed their disdain at being represented by the national anthem of the People's Republic of China.

Such disrespect of the "March of the Volunteers" will soon be illegal, as Hong Kong moves to adopt a hugely controversial national anthem law which critics say could undermine its constitutional protections for free speech.

Lawmakers Wednesday, January 23 began discussing the legislation which sets standards for playing and singing "March," and makes it a crime punishable by up to three years in prison "to insult the national anthem," CNN says.

Schoolchildren, including those at international schools, would also be legally required to learn the anthem, which opens with the line, "Arise, we who refuse to be slaves!"