Croatians have voted to ban gay marriage.

A majority of residents in the strongly Roman Catholic country voted yes to changing the constitution to define marriage as the union between a man and a woman.

Hundreds of gay rights supporters demonstrated in Croatia's capital Zagreb on Saturday ahead of the vote, while 700,000 signed a signature pledging their support to ban gay marriage.

Some 64 percent approved the ban and 34 percent voted against it, with 60 percent of the votes counted, the election office said on its website.

The yes vote effectively bans any future possibility of approving gay marriage.

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The constitutional amendment is supported by at least 104 members of the 151-seat parliament, according to the BBC.

In a poll on state-television channel HRT, 59 percent of Croatians said they would vote "yes." Other polls have put that support at 70 percent of the vote.

The government in power opposes the amendment, including Prime Minister Zoran Milanovic,

The "yes" campaign, known as "In the Name of the Family," has been led by the church and has support from opposition parties in government. About 90 percent of Croatia's 4.4 million people are Roman Catholic.

Croatia became the 28th member of the European Union in July.

Some Croatians worry that banning gay marriage will have a negative impact on tourism, a $9.5 billiion industry that accounts for a fifth of the country's economic output.

"It’s not good for Croatia to establish itself as a country of intolerance,” Prime Minister Milanovic told reporters in Zagreb on Saturday.