DENVER (AP) - Civil unions for gay couples were signed into law in Colorado, ending a dramatic turnaround in a state where voters banned same-sex marriage in 2006.
Colorado will join eight US states that have civil unions or similar laws. Nine states and the District of Columbia allow gay marriage. The law takes effect on May 1.
Hundreds looked on as Democratic Governor John Hickenlooper signed the bill, with many chanting "Equal! Equal!"
"There is no excuse that people shouldn't have all the same rights," Mr Hickenlooper told the crowd.
Views on gay rights have been rapidly shifting in the United States. A Pew Research Centre survey found that 49 per cent of Americans favour allowing gays and lesbians to marry legally, and 44 per cent are opposed. A decade ago, 58 per cent opposed it and a third supported it.
Civil unions grant gay couples rights similar to marriage, including enhanced inheritance and parental rights. People in civil unions also would have the ability to make medical decisions for their partners.
"It means I can change my name finally," said 21-year-old Amber Fuentes, who plans to have a civil union with Ms Yolanda Martinez, 34.
US Supreme Court is expected to rule on California's gay marriage ban in the coming months, a decision that could affect the status of gay marriage other states.
"It's really meaningful. To have the recognition of your love and relationship just like any other relationship by the state is an important both legal and symbolic thing," said Democratic House Speaker Mark Ferrandino, a sponsor of the bill and the first openly gay lawmaker to hold the title of speaker in Colorado.
Most Republicans opposed the bill, saying they would have liked to see religious exemptions to provide legal protections for those opposed to civil unions. Churches are shielded under the new law, but Democrats rejected protections for businesses and adoption agencies, arguing the Republican suggestions were too broad and could provide legal cover to discriminate.