Conservative Christian groups in South Korea protested a Lady Gaga concert on Friday, saying it was “pornographic” and promoted homosexuality.

Gaga is kicking off the Asian leg of her Born This Way tour in Seoul and sang in the capital city's Olympic Stadium on Friday evening. Approximately 45,000 fans watched her perform hits like Poker Face and Judas.

However, as fans were lining up to get into the show, a group calling itself the Civilians Network against the Lady Gaga Concert gathered outside the stadium and called on her to cancel her appearance.

South Korea's government had already bowed to public pressure and banned fans under the age of 18 from attending the concert.

At issue is Lady Gaga's stance in favour of empowering gay men and women, which she promotes in her song Born This Way and her foundation.

Lady Gaga fans in Seoul arrived for Friday's concert dressed as the singer. (Kim Hong-Ji/Reuters)

"Some people can accept this as another culture, but its impact is huge beyond art and debases religions," said protest leader Rev. Yoon Jung-hoon, according to Reuters.

"Even adults can't see her performance, which is too homosexual and pornographic."

The protest group has threatened a boycott of Hyundai Card, sponsor of the concert, and its parent company, Hyundai Motor Co, which is South Korea's largest car-maker.

Yoon said he would attend the concert to monitor its content. South Korea has approximately 14 million Christians and many take a hardline view against homosexuality, calling it an immoral lifestyle.

Ahead of Friday's concert, Lady Gaga posted a message on Twitter, saying: "Nervous for tonight. Hope I make little monsters happy and proud."

"I can you hear you Korea. I'm shaking," she tweeted before starting the concert.

Gaga potentially faces further backlash from other religious groups as the tour continues. Her upcoming stops include Hong Kong, Taipei, Manila, Singapore and Jakarta over the next few weeks, before she heads to Australia and New Zealand.

"I call on Lady Gaga to respect our cultural and traditional values. Most people here are Muslims and we cannot tolerate her revealing outfits and sexy performances," Amidhan, leader of Indonesia's Muslim clerical body the Ulema Council, told Agence France-Presse.

"It's better for Lady Gaga to cancel her show in this country if she has no willingness to respect our demand. Please do not destroy our nation's morality and ruin our dignity."