Gay couples are lining up in Salt Lake City, Utah, to be married hours after a US judge ruled the state's ban on gay unions is unconstitutional.
The county clerk began issuing the licences, despite state officials saying they would appeal and seek a order to prevent further marriages.
Judge Robert Shelby ruled a voter-passed 2004 ban violated same-sex couples' rights to equal protection.
The ruling comes the same week New Mexico legalised gay marriage.
That state's highest court ruled it was unconstitutional to deny marriage licences to same-sex couples.
The first gay couple to be married in Utah, Michael Ferguson and Seth Anderson, did so about an hour after the ruling was posted.
Among the dozens of same-sex couples lined up to get marriage licences at the Salt Lake County clerk's office was State Senator Jim Dabakis.
The chairman of the state's Democratic party, was there with his longtime partner, Stephen Justesen.
"I waited 27 years," Mr Dabakis told the Associated Press. "We didn't want to get married until we could get married in Utah."
The case was brought by three couples who were denied licences or recognition in the state, including one couple who had been legally married in Iowa.
In his ruling, Judge Shelby said Utah failed to show allowing gay marriages would affect opposite-sex unions.
"In the absence of such evidence, the state's unsupported fears and speculations are insufficient to justify the state's refusal to dignify the family relationships of its gay and lesbian citizens," he wrote in the ruling.
In a statement, the Utah Attorney General's office said it was requesting an emergency stay "pending the filing of an appeal".
Such an order would put same-sex marriages performed on Friday in legal limbo until the case is decided in a higher court.
And Governor Gary Herbert said he was "very disappointed an activist federal judge is attempting to override the will of the people of Utah".
"I am working with my legal counsel and the acting attorney general to determine the best course to defend traditional marriage within the borders of Utah."
The state passed the ban in 2004 with 66% of the vote.