Singapore has annulled the marriage of a transgender woman and her partner.

The couple married as a man and woman in 2015 and  the husband later underwent sex change surgery to become a female, according to local daily the Straits Times.

Their marriage was voided by officials in February after the couple informed authorities of the sex change when applying for a flat for married couples, the report added.

It was one of three voided by the Registry of Marriages (ROM) to date, in a little-known proceeding that has caught family lawyers by surprise. The three unions were voided "for reasons including impersonation by one party", an ROM spokesman told The Straits Times.

"Singapore law does not recognise a marriage where both parties are of the same sex. At the point of marriage, a couple must be man and woman, and must want to be and want to remain as man and woman in the marriage," he added.

The couple reportedly missed out on buying a government-subsidised flat for married couples and were forced to move into a smaller, more expensive apartment.

Lawyers in Singapore have questioned the marriage registry’s authority to annul marriages without going to court.

According to The Straits Times, family lawyer Sim Bock Eng said: “There is no requirement that parties must remain of the same gender throughout the marriage, nor is there any provision that such marriages (where parties undergo gender reassignment after marriage) are void.”