Thirty-one same-sex marriages were expected to take place throughout New Zealand as the law took effect on Monday.
The country's parliament amended the Marriage Act back in April.
The New Zealand activist group Campaign For Marriage Equality hailed the introduction of the new law, saying it ended a historical injustice.
"A massive congratulations to the happy couples tying the knot today. Marriage equality has finally arrived in New Zealand," spokesman Conrad Reyners said.
Enquiries about holding same-sex weddings in New Zealand have come in from around the world, including Russia, the United States, Hong Kong, Britain, Singapore, Malaysia, Guyana and Burma.
Among the first to be married was an Australian couple who wed even though their marriage will not be legally recognized at home. Paul McCarthy and Trent Kandler won a Tourism New Zealand competition to take part in the ceremony.
McCarthy said he hoped the day would come when his marriage would be legally valid in Australia, and said the ceremony had shown that same-sex married couples were "not freaks [and] that there's nothing to fear from marriage equality."
Some 1,000 same-sex couples in Australia say they plan to travel to New Zealand to marry, according to the Australian Marriage Equality lobby group. A marriage equality bill was recently voted down by Canberra.
Not everyone approves of the new marriage law, with conservative groups and the Anglican Church voicing concern.
The conservative lobby group Family First called the change to the Marriage Act "an arrogant act of cultural vandalism."
"Social engineers including politicians and activists are expecting marriage supporters to drop their deeply held convictions because of the misguided decisions of policitians," national director Bob McCoskrie said.
The Anglican Church has asked its ministers not to conduct same-sex weddings for the time being, pending a report to its general synod next year.
New Zealand decriminalized homosexuality in 1986 and has allowed same-sex civil unions since 2005.
The countries that currently allow same-sex marriages are Argentina, Belgium, Brazil, Canada, Denmark (with the exception of the Faroe Islands and Greenland), France, Iceland, Netherlands (with the exception of Aruba, Curaçao and St Maarten), New Zealand (with the exception of Tokelau, Niue and the Cook Islands), Norway, Portugal, Spain, South Africa, Sweden and Uruguay. Parts of Mexico and the United States also allow same-sex couples to marry.
tj/pfd (AFP, dpa)