SINGAPORE - The police are looking into a viral video of a concertgoer heard shouting a gang slogan during South Korean girl group Twice's concert on Sunday (June 17).

A seven-second clip of the incident was shared online recently, after it was first posted on Twitter.

In the video, a voice could be heard chanting "sah lak kau", or "369" in Hokkien, as the nine-member K-pop group sang and danced on stage.

The slogan is synonymous with the gang Sio Kun Tong. The concertgoer's face was not shown in the video.

In response to queries, the police said they are aware of the incident and are looking into it.

Under the Societies Act, it is illegal to join or act as a member of an unlawful society. It is also illegal to attend a meeting of an unlawful society.

The Twitter user who first uploaded the video claimed the voice in the clip belonged to his brother and that he had shouted the gang slogans during the concert, as he did not know the words to a fan chant being sung by other concertgoers.

About 8,500 fans turned up for the three-hour concert, Twiceland Zone 2: Fantasy Park, at the Singapore Indoor Stadium on Sunday.

The group performed hits such as Cheer Up, TT and Knock Knock in their second concert in Singapore, after their debut gig in 2017.

Related Story K-pop girl group goes Twice as big for second Singapore concert

The police have previously taken action against those who chanted gang slogans in public.

In November 2017, four men were charged for their alleged involvement in unlawful societies, after videos of them shouting gang slogans at funeral processions were circulated online.

That same month, five men were arrested for their suspected involvement in gang-related activities at Envy Dance Club in St James Power Station. The police said they had been alerted to an online video showing several men shouting gang-related slogans.

Anyone convicted of being a member of an unlawful society may face a fine not exceeding $5,000, a jail term of up to three years, or both.