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San Francisco's new Mayor, Gavin Newsom, decided earlier this week to lift the ban on single-sex marriages in the city.

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The first couple to tie the knot were long-time lesbian activists Phyllis Lyon and Del Martin. They had been together for 51 years on Valentine's Day.

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Couples celebrated the nationally unprecedented weddings at a reception in the city hall.

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Officials estimated that hundreds of licences were issued as couples streamed into the city hall.

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They said they would keep marrying gays and lesbians all over the Valentine's Day weekend.

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The weddings in San Francisco have encouraged gay couples elsewhere in the US to demand the right to marry.

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But not everyone is in favour of single-sex marriages. A number of legal challenges are expected.