LOS ANGELES - CALIFORNIA'S vote to ban same-sex marriages in a referendum will be contested by activists and city officials who have lodged multiple legal challenges to the ballot, officials said on Thursday.

In a stunning result, voters approved a proposal added to ballot papers in Tuesday's presidential election which amended the state constitution to say that only marriages between men and women are recognised in California.

Voters approved the constitutional amendment by a margin of 52.5 to 47.5 per cent, according to near-complete results.

The decision came only six months after California's Supreme Court overturned a previous ban on same-sex marriage, paving the way for thousands of gay and lesbian couples to tie the knot in the state.

However opponents of same-sex marriage successfully gathered enough support for an amendment to be added to the Nov 4 election which sought to override the California Supreme Court decision.

Now activists and city officials in Los Angeles and San Francisco are vowing to return to the California Supreme Court, arguing that the vote - known as 'Proposition 8' - represented a sweeping revision of the constitution and was more far-reaching than a simple amendment.

'A major purpose of the constitution is to protect minorities from majorities,' said Ms Elizabeth Gill, an attorney with the American Civil Liberties Union (ACLU), one of the rights groups fighting the ban.

'Because changing that principle is a fundamental change to the organising principles of the constitution itself, only the legislature can initiate such revisions to the constitution.'

Challenges have been filed by the ACLU, the National Centre for Lesbian Rights and Lambda Legal while San Francisco, Los Angeles and Santa Clara have sued in a joint bid.

'Equal protection of the laws is not merely the cornerstone of the California Constitution, it is what separates constitutional democracy from mob rule tyranny,' San Francisco City Attorney Dennis Herrera said in a statement.

Another lawsuit has been filed by Los Angeles lawyer Gloria Allred on behalf of the lesbian couple whose legal fight initially led to May's Supreme Court decision to overturn a previous ban.

The marriage ban sparked angry protests in California on Wednesday, with thousands taking to the streets in Los Angeles to condemn the ban.

Angry crowds thronged the streets in central West Hollywood, the heart of Los Angeles' gay community, chanting slogans and waving signs.

The legal status of thousands of same-sex couples who have wed since June remains unclear although state officials have insisted that the marriages will remain valid. -- AFP