Chief Secretary Eric Chan said on Sunday it's ridiculous and unbelievable that there have been repeated mistakes involving the national anthem at international rugby matches involving Hong Kong.

It's emerged that the name of a song associated with violent protests in 2019 appeared on screen during television broadcasts as the anthem played at two rugby World Cup Qualifiers this year.

The Hong Kong Rugby Union (HKRU) said the organiser, World Rugby, had apologised for the mistake and attributed the error to a "graphics operator".

The blunders came to light after the protest song was played in place of the "March of the Volunteers" at a sevens tournament organised by Asia Rugby last week in South Korea.

"These things are really ridiculous. We're very dissatisfied that they keep happening. We will write to World Rugby and Asia Rugby to express strongly our dissatisfaction, and demand a full investigation from them, to give an account to us of what happened," Chan told reporters after attending an event.

He said the police will investigate thoroughly and look into whether any crimes have been committed, and the government will demand the HKRU formulate measures going forward to avoid a repeat of the incidents, such as providing organisers with clear descriptions of the national flag and anthem.

The chief secretary stressed that the government can't understand how the blunders happened, given the experience both of the organisers have in staging such events.