North Carolina voters approved a constitutional amendment on Tuesday defining marriage solely as a union between a man and a woman, becoming the latest US state to effectively slam the door shut on same-sex marriages.

With most of the precincts reporting on Tuesday, unofficial returns showed the amendment passing with about 61 percent of the vote to 39 percent against. North Carolina is the 30th state to adopt such a ban on gay marriage.

Tami Fitzgerald, who heads the pro-amendment group Vote FOR Marriage NC, said she believes the initiative awoke a silent majority of more active voters in the future.

'I think it sends a message to the rest of the country that marriage is between one man and one woman,' Fitzgerald said at a celebration Tuesday night. 'The whole point is simply that you don't rewrite the nature of God's design based on the demands of a group of adults.'

In the final days before the vote, members of President Barack Obama's Cabinet expressed support for gay marriage and former President Bill Clinton recorded phone messages urging voters to oppose the amendment.

Supporters of the amendment responded with marches, television ads and speeches.

North Carolina law already bans gay marriage, but an amendment effectively seals the door on same-sex marriages.

The amendment also goes beyond state law by voiding other types of domest.