The California Supreme Court on Thursday voted, 5 to 2, to nullify about the 3,995 same-sex marriages performed between Feb. 12 and March 11 in San Francisco. According to reports, the justices found that Mayor Gavin Newsom had overstepped his authority in granting marriage licenses to lesbian and gay couples in defiance of state law.

The seven justices said the mayor's decision to issue the licenses and perform the ceremonies violated a 1977 state law that defines marriage as a union between a man and woman.

The court focused its ruling on the limits of local government authority, and avoided the larger constitutional question of whether the state can limit marriage to a union between a man and a woman under the California Constitution.

Chief Justice Ronald George noted the ruling did not address "the substantive legal rights of same-sex couples" but insisted local officials could not legislate state law from city halls or county government centres.

"Local officials in San Francisco exceeded their authority by taking official action in violation of applicable statutory provisions," he wrote. "The same-sex marriages authorised by the officials are void and of no legal effect."

Despite the ruling, Mayor Newsom declared victory and said his fight for equal rights has put a human face on discrimination for the world to see.

"Now we have these 4,000 couples to tell their stories. We have their immediate family, their extended family, their grandparents, their sons, their daughters, their cousins, aunts and uncles," Newsom told the media in a City Hall room.

"So I'm not in any way discouraged. I'm frankly more resolved."

At the news conference, he said that it's only a matter of time that San Francisco would prevail much like other civil rights activists who fought laws banning interracial marriage four decades ago.

"No irreparable harm was done," when gay and lesbian couples were married earlier this year, he said. "The sky didn't fall in. The world did not come to an end. The institution of marriage did not end because of these actions. There were no riots."

In February, the mayor ignited a fiery nationwide debate by allowing same-sex couples to wed over a four-week period before the California high court halted them.

In May, Massachusetts became the first U.S. state to allow gay marriage. The debate will continue to rage ahead of the November presidential elections and is up for review in many court cases.

Several lawsuits have been consolidated in San Francisco Superior Court, filed by the city, same-sex couples and various civil-rights groups. Those cases are expected to be decided this year by a trial judge and eventually force the state Supreme Court to address the heart of the legal battle.