Three people were arrested for turning their backs and remaining seated when China's national anthem was played prior to Hong Kong's home World Cup qualifier against Iran, police said Friday.

Football fans in Hong Kong used to boo the national anthem as a show of political discontent, but the government in 2020 banned the practice as part of a wider crackdown following huge democracy protests in the city.

At Hong Kong Stadium on Thursday police said two men and a woman were arrested because they "turned their backs toward the pitch and did not stand for the playing of the national anthem".

"Police stressed that anyone who publicly and intentionally insults the national anthem in any way commits a crime," a statement said.

The three arrested were between the ages of 18 and 31. If convicted they face up to three years in jail and a fine of HK$50,000 ($6,400).

Hong Kong, whose hopes of reaching the next stage of qualifying for the 2026 World Cup were already over, went on to lose the game to Iran 4-2.

Hong Kong is a special administrative region of China but competes in its own name in many international sports, including football.

During the politically tumultuous 2010s, the Hong Kong team became a vessel for civic pride and occasionally anti-government sentiment.

At the time, the Chinese national anthem was routinely drowned out by boos before Hong Kong matches, enraging local and mainland officials.

Soon after Beijing imposed a sweeping national security law on Hong Kong in 2020, the finance hub passed a separate local law criminalising insults towards the anthem.