Australians who are neither male nor female can categorize their gender as "x" in their passports as the government has made the option official in the document.

The new passport feature is for the benefit of people who have trouble when going abroad because their appearance does not match their gender, according to Senator Louise Pratt.

"It's a really important recognition of people's human rights that if they choose to have their sex as ‘indeterminate', they can," Dailymail.com quoted her as saying.

Pratt, whose partner was born female but now lives as a man, acknowledged that there are people with genetically ambiguous gender but were arbitrarily assigned the "male" or "female" sex at birth.

"There have been very many cases of people being detained at airports by immigration in foreign countries simply because their passports don't reflect what they look like," BBC quoted her as telling Australian radio.

For his part, Foreign Minister Kevin Rudd regards the amendment as a relief that will ease the life and administrative burden of sex and gender diverse people who want an appropriate gender in their passport that matches their physical appearance.

The passport amendment was pursued by Peter Hyndal on behalf of human rights advocacy group A Gender Agenda, a Canberra-based community group that provides support, education and advocacy for sex and gender diverse people.

The passport does not allow transgenders to choose 'x.' Instead, they will have to choose either "male" or "female."