California is due to become America's gay marriage capital - if only for a short time - after an historic court verdict that religious groups have vowed to overturn.

Yesterday's decision by the Californian Supreme Court opens the door for same-sex couples to hold marriage ceremonies in a month's time. Unlike Massachusetts, which is the only other state with legalised gay marriage, residents from all over the United States will be permitted to have their unions in California, leading to the possibility of people coming from throughout America to the state.

Arnold Schwarzenegger, the California Governor, who is known to oppose the move, said he would respect the court's verdict.

Christian and conservative groups vowed to appeal for a stay of the decision until after a proposed November vote on a constitutional amendment which would bar same sex marriage. However getting a motion before the court may take several weeks, leaving same-sex couples a small window in which to tie the knot.

In its 4-3 ruling, the Republican-dominated High Court struck down state laws against same-sex marriage and said domestic partnerships as they stand, which provide many of the rights and benefits of matrimony, are insufficient.

"In contrast to earlier times, our state now recognises that an individual’s capacity to establish a loving and long-term committed relationship with another person and responsibly to care for and raise children does not depend upon the individual’s sexual orientation," Chief Justice Ronald George said.

The ruling would make California the second state, after Massachusetts in 2004, to allow same-sex couples to get married.

Since Massachusetts passed its verdict, more than 9,500 gay and lesbian couples have taken advantage of the law. But the California ruling is considered monumental by virtue of the state’s size - 38 million out of a US population of 302m - and its historical role as America's gay and lesbian capital, with San Francisco at the forefront. California has an estimated 108,734 same-sex households, according to 2006 census figures.

Crucially, unlike Massachusetts, California has no residency requirement for obtaining a marriage license, meaning gays nationwide are likely to flock to the state to get married. However, since most states do not recognise same-sex marriages performed elsewhere, the ruling's reach could be limited.

Religious communities immediately vowed to oppose the verdict. The Alliance Defence Fund said it would ask the justices to postpone putting the verdict into effect until after the proposed November ballot. California’s secretary of state is expected to rule by the end of June whether the sponsors of the ballot measure gathered enough signatures to go ahead with the vote.

"We’re obviously very disappointed in the decision. The remedy is a constitutional amendment. The constitution defines marriage as a union between one man and one woman," said Glen Lavy, senior counsel for the organisation.

Attorney General Jerry Brown, whose office had argued to uphold the ban, said he would nevertheless work with Governor Schwarzenegger and state agencies to implement the ruling.

The case was set in motion in 2004 when the mayor of San Francisco threw City Hall open to gay couples to get married in a calculated challenge to California law. Four thousand wed before the Supreme Court put a halt to the practice after a month. Two dozen gay couples then sued, along with the city and gay rights organisations.

A spokesman for Republican John McCain, who opposes gay marriage, said the Arizona senator "doesn’t believe judges should be making these decisions." The campaigns of Democrats Barack Obama and Hillary Clinton said they believe that the issue of marriage should be left to the states.

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