Some airlines are introducing extra gender options for LGBT passengers

British Airways and Air New Zealand have joined a wave of major U.S. airlines planning to introduce extra gender options for LGBT+ passengers who don't identify as either male or female.

LGBT+ groups have welcomed the change, saying it would smooth the way for many trans, intersex and non-binary passengers - or those who simply don't look typically male or female - who have long faced discrimination when flying.

"It's a big move", Julia Ehrt, of the International Lesbian, Gay, Bisexual, Trans and Intersex Association (ILGA), told the Thomson Reuters Foundation.

"Persons presenting as gender non-conforming or trans persons who might not have been able to change their name or gender markers in passports regularly have serious challenges in travelling.

"That can range from being challenged about your gender marker or first name upon check-in or at security, through to outright denial of being able to board a plane."

Global aviation body the International Air Transport Association (IATA) recently released new guidance for airlines who want to offer non-binary gender options for passengers.

Typical examples of non-binary markers could include a X or 'undisclosed' instead of male or female, and the gender-neutral title Mx instead of Mr or Mrs.

Several major U.S. airlines including United, American Airlines and Delta have confirmed they are preparing to bring in more gender options in the wake of the new guidelines.

Now British Airways and Air New Zealand say they are planning to follow suit.

"We know how important it is for all of our customers to feel comfortable and welcome no matter how they self-identify," a spokesman for British Airways said on Wednesday.

"We are working to change our booking platform to reflect this."

Air New Zealand said it was "exploring how we can introduce non-binary gender options across our various digital environments".

The Lufthansa Group, which owns Lufthansa, SWISS and Austrian Airlines, told the Thomson Reuters Foundation it was "taking the implementation of additional gender options into consideration".

Up to 1.7 percent of people are intersex - meaning they are born with sex characteristics that are neither definitively male or female - according to the United Nations.

In addition, studies suggest that a growing number of people identify as trans or non-binary.

More than 10 percent of U.S. adults identify as LGBT+, rising to 20 percent among younger millennial, found a 2016 study by LGBT+ group GLAAD which argued that youth increasingly reject binary identities such as male or female.

Experts said airlines would be looking to adapt to changing demographics and social norms.