A mainland law student was on Tuesday jailed for six months after pleading guilty to a colonial-era sedition offence over plans to unfurl a banner featuring the "Pillar of Shame" in Causeway Bay on June 4.

West Kowloon Court heard that Zeng Yuxuan, 23, had planned on displaying the nine-metre long banner on a footbridge, but was arrested before she could carry out the act.

Zeng pleaded guilty at West Kowloon Court to attempting or preparing to act with seditious intention.

In sentencing, chief magistrate Peter Law said the defendant was part of an international plan to display similar banners in multiple cities across the globe on June 4, and had received the banner from a mainland dissident.

Law said the defendant had a detailed plan and did not act out of impulse, and added that the scale and collective nature of the plot meant the negative impact would be far greater than if she had acted alone.

Zeng had also been accused of commemorating a man who stabbed a policeman outside the Sogo department store in Causeway Bay in 2021. Prosecutors said this was also a seditious act, but they later dropped the charge.