The case was brought by a transgender man, known as "K", who was encouraged by doctors to use men's public bathrooms as part of his gender dysphoria treatment.

K's Hong Kong ID card still identified him as female, which meant he could be fined up to HK$2,000 ($255) under existing rules.

He argued that this breached his rights to equality, privacy, and to be free from discrimination.

High Court judge Russell Coleman agreed and struck down two provisions in the city's regulations, giving the government a year to make the change.

Transgender activists in the financial hub have notched several wins over the past decade in Hong Kong courts, which are separate from those in mainland China.

The city's top court decided in 2023 that it was unconstitutional for the government to require a person to complete full gender-affirming surgery before the "sex entry" on their ID card could be changed.

This decision meant the government had largely conceded its case in the public toilets legal battle, Coleman wrote on Wednesday.

K did not challenge the constitutionality of sex-segregated public toilets.

He was undergoing hormone treatment pending surgery when he launched the legal challenge.

His treatment required that he undergo "real life experience" including using public toilets that match his identified gender, according to the ruling.

"Many trans people choose not to use public conveniences at all, due to fear, the threat of harassment, and to avoid having their gender identity invalidated or undermined," Coleman wrote.

AFP has contacted K's legal team for comment.