HONG KONG (AFP) - Hong Kong's highest court on Monday began hearing the final appeal of a transsexual woman who is seeking to wed her boyfriend, in a potentially groundbreaking case for the Chinese city.

The woman, who was born as a man, is known only as "W" under anonymity rules and now in her 30s.

She is seeking to overturn earlier rulings that said marriage is only allowed between couples who were of the opposite sex at birth.

She has argued that she has undergone government-subsidised sex change surgery and had her gender altered on her identity card since she launched the legal battle - the first such case in Hong Kong - in 2010.

The city's Registrar of Marriages had ruled that W could not marry her boyfriend because her birth certificate - which cannot be changed under Hong Kong law - says that she is still a man.

"We say the laws of marriage can and should recognise that sexual identity can change," W's counsel David Pannick told the court in his opening arguments.

"The right to marry is fundamental... the birth certificate is a record of historical facts," he said, adding that W is now "medically, psychologically and socially" a woman.

The lawyer said the Registrar of Marriages should recognise his client's new gender, which is stated in official documents like her identity card and passport, and a denial of her bid to marry violates her constitutional rights.

W was not present in court on Monday. The government lawyers will also make their submissions at the two-day hearing that will last till Tuesday.

The government's counsel has previously argued that existing laws did not accommodate transsexual marriage.

W is one of a small number of people to have undergone sex reassignment surgery in Hong Kong, where activists say sexual minority group like homosexuals and transsexuals still face widespread discrimination.

The city's gay community has also pushed for the recognition of same-sex marriage, which is not legal in Hong Kong.

In throwing out W's case in 2010, the a court said there was insufficient evidence "to demonstrate a shifted societal consensus in present-day Hong Kong regarding marriage to encompass a post-operative transsexual".