Lawmakers in the northwestern US state of Washington voted in favor of a bill legalizing same-sex marriage, which should soon be signed into law by the governor, officials said.

Governor Christine Gregoire has five days to approve the text, which would make Washington the seventh state in the nation to allow gay marriage.

"The bill was passed by the House on a 55-43 vote," an official in Washington's House of Representatives in the state capital Olympia told AFP.

Gregoire "has five days after she gets the bill. It will probably take a few days to get it over to her, and then she has five days," said the official, who asked not to be named.

The governor said last month she supported the bill and that she planned to sign it if approved by lawmakers. Washington's state senate approved the bill last week.

Six US states -- Connecticut, Iowa, Massachusetts, New Hampshire, New York and Vermont -- plus the District of Columbia already allow same-sex marriage, but the issue remains highly controversial.

A group of 80 US mayors -- including New York's Michael Bloomberg, Chicago's Rahm Emanuel, Antonio Villaraigosa from Los Angeles and Annise Parker from Houston -- last month unveiled a campaign to win support for same sex marriage.

The vote in Washington state comes the day after a US federal appeals court struck down a California law that had stripped gays and lesbians of the right to marry.

Gay marriage was briefly authorized in California in 2008, but later banned by a referendum on what was known as Proposition 8. It rewrote the state's constitution to restrict marriage to unions between a man and a woman.

On Tuesday, the three-judge appeals panel in San Francisco ruled 2-1 that a lower court had properly declared the ban a violation of the US Constitution.