The United Nations (UN) has celebrated Wonder Woman's 75th birthday by naming the comic book character as its new honorary ambassador for the empowerment of women and girls, despite frustration from both inside and outside the world organisation that the spot should go to a real and less-sexualised woman.

The ceremony, at the Economic and Social Council chamber, was marred by some 50 UN staffers who silently turned their back to the stage, some with their fists in the air.

The super heroine's image will be used by the UN on social media platforms to promote women's empowerment, including on gender-based violence and the fuller participation of women in public life, using the hashtag #WithWonderWoman.

The push, hoping to reach young people, is backed by DC Entertainment and Warner Bros, which produce both comics and films featuring Wonder Woman.

But an online petition, started by UN staffers, asked the Secretary General to reconsider the appointment, saying: "The message the United Nations is sending to the world with this appointment is extremely disappointing".

As of Friday afternoon, it had more than 1,000 signatures.

About 50 UN staffers silently turned their back to the stage, some with their fists in the air. ( AP: Bebeto Matthews )

Winnie the Pooh, Tinker Bell previous ambassadors

Honorary ambassadors, as opposed to goodwill ambassadors like Nicole Kidman and Anne Hathaway, are fictional characters.

The UN previously tapped Winnie the Pooh to be an honorary ambassador of friendship in 1998 and Tinker Bell as the honorary ambassador of green in 2009.

The event brought together actress Lynda Carter, who played Wonder Woman in the 1970s TV series, and Gal Gadot, who has taken on the role in the forthcoming Wonder Woman film, as well as Girl Scouts in Wonder Woman t-shirts and UN staffers' kids who skipped school.

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Diane Nelson, president of DC Entertainment, gave a speech in which she argued even comic book stories could "inspire, teach and reveal injustices".

Carter, who gave a moving speech about how Wonder Woman embodies the inner strength of every woman, was the only one to acknowledge the protesters in her remarks.

"Please embrace her. To all those who don't think it's a good idea, stand up and be counted," she said.

Afterwards, she said: "It's OK that not everyone agrees, but get over it and say: 'What else is new?'"

Lynda Carter played Wonder Woman in the 1970s. ( Supplied: Imdb/AP )

The actress noted she had weathered criticism of the role for years:

"In the beginning, in the 70s, it was 'Well, she's objectified'. It's like: 'She's too tall, she's too this, she's too this. Oh, she wants to be a feminist?'"

Gadot said after the event: "I'm the kind of person who always looks at the half-full glass. I care for the people who care and I'm here for a wonderful cause today".

"That's all what my focus is."

'Why a sexualised cartoon character?'

But among those thinking the glass was half empty was Shazia Z Rafi, who previously worked at the UN and is now managing director of consulting firm Global Parliamentary Services.

She argued the choice of Wonder Woman was tone-deaf at a time when real women are fighting against sexual exploitation and abuse.

"I think it's a lot of rubbish that you can appoint a cartoon female to represent gender equality in this day and age, even if it is to reach younger women," she said.

"I'm not against cartoons. I think cartoons have a value. But that is not the issue."

Gal Gadot has taken on the role in the forthcoming Wonder Woman film. ( Supplied )

Ms Rafi said there were plenty of real heroines that could be the face for gender equality, including Nadia Murad, who has become the public face of the thousands of Yazidi women and girls who remain in sexual slavery, and Malala Yousafzai, who defied the Taliban to demand that girls be allowed to receive an education.

UN employee Elizabeth Leff said: "Why do we need to use a sexualised cartoon character?"

The Wonder Woman appointment came after many women were dismayed that another man, former prime minister of Portugal Antonio Guterres, was chosen to be the next secretary-general.

Over 50 countries and many organisations lobbied for a woman and seven of the 13 candidates to replace Ban Ki-moon on January 1 were women, but none placed above third in the six informal polls.

Ms Rafi, who had campaigned for a woman to be appointed the world's diplomat-in-chief, called it a "slap in the face of all women who work within the UN".

She said the decision to name Wonder Woman as an ambassador was effort to appease disappointed staffers.

Ms Rafi and the petition also took issue with Wonder Woman's skimpy outfit, arguing the world might not embrace a scantily clad character in a shimmery, thigh-baring body suit with an American flag motif and knee high boots.

"This whole issue of taking a cartoon figure who is clad in a bustier, with cleavage, high-cut shorts, a sort of muscled version of a Barbie, and saying 'this is what represents gender equality' is incredible," she said.

"It's culturally insensitive. It's insulting."

It is not the first time the UN has partnered with a huge media company.

In March, the UN appointed Red, the leader of the Angry Birds mobile game characters, as an envoy to tackle climate change, in partnership with Sony Pictures Entertainment.

AP/Reuters