A court has accepted China's first same-sex marriage case, lodged by a gay man against a civil affairs bureau for denying him the right to marry, in a decision hailed as a step forward for gay rights.

While homosexuality is not illegal in China, and large cities have thriving gay scenes, same-sex marriage is not legal and same-sex couples have no legal protections.

Sun Wenlin, 26, told Reuters a court in Changsha, the capital of Hunan province, had accepted his lawsuit on Tuesday.

"I think from a legal point of view, we should be successful," Sun said.

"Our marriage law says there is the freedom to marry and gender equality. These words can be applied to same-sex marriage."

Sun said he had filed the lawsuit in December because he wanted to form a family unit with his 36-year-old partner.

Sun said he had tried to register to marry his boyfriend at the Furong district civil affairs bureau in June but was rejected by an official who told him "marriage had to be between a man and woman".

Officials at the Furong district civil affairs bureau could not be reached for comment and a court official in Furong, where the case will be heard, said the court "will not comment on cases before they are heard".

China is becoming more tolerant of homosexuality, which until 2001 was listed as a mental disorder, but many gay people remain under heavy pressure to stay in the closet.

Activists said the court's acceptance of the case was significant and would likely lead to more such cases.

"In China, courts often reject politically sensitive cases, so the fact that the lawsuit is accepted signals some official willingness to address discrimination against LGBT (lesbian, gay, bisexual and transgender) people, which is encouraging," said Maya Wang, a China researcher at New York-based group Human Rights Watch.

"But we will need to see if they actually win the case. If they do, it'd be a truly watershed moment for LGBT rights in China."

Sun's legal consultant, surnamed Ding, said the case would be heard within six months.

"From the standpoint of improving visibility, this case is no doubt a victory," said Ding, who declined to give her full name because of the sensitivity of the matter.

Lu Jun, co-founder of anti-discrimination group Yirenping, said the case would bring more such legal action.

"More people will know that marriage registration is a right," Lu said.