After waiting years and seeing marriage rights nearly awarded and then retracted, gay couples in Maine's largest city did not have to wait a moment longer than necessary to wed, with licences issued at the stroke of midnight as the law went into effect.

Among them were Steven Bridges and Michael Snell, who held a commitment ceremony six years ago but wanted to make their marriage official under state law.

"It's historic. We've waited our entire lives for this," said Mr Bridges, a retail manager, who's been in a relationship with Mr Snell, a massage therapist, for nine years.

Mr Bridges, 42, and Mr Snell, 53, wore lavender and purple carnations on black T-shirts with the words Love is love.

More than a dozen couples stood in line to get marriage licenses at Portland City Hall early today. There were free carnation boutonnieres, and a jazz trio played.

With Mr Snell's two adult daughters looking on, they exchanged their vows in the city clerk's office after getting the first marriage licence issued to a same-sex couple in Portland.

They said they will hold another ceremony with friends this summer, after the weather warms up.

Voters approved gay marriage in November, making Maine and two other states the first to do so by popular vote.

The law is already in effect in Washington state; Maryland's takes effect on Tuesday, the first day of 2013.

Gay marriage was already legal in New York, Connecticut, Iowa, Massachusetts, New Hampshire, Vermont and the District of Columbia, but those laws were either enacted by politicians or through court rulings.

The Maine Legislature had once approved same-sex marriage, but it was overturned by a state-wide referendum three years ago, crushing couples who had already made wedding plans.

Gay marriage supporters collected signatures to put it on the ballot again, and this time it was easily approved.