More than 60% of Slovenians have voted against legalising gay marriage in a referendum marked by low turnout, according to near-complete results from the electoral commission.

Just 35.65% of registered voters turned out to have their say on whether the country should approve legislation - already passed in parliament - that would have given gay couples the right to marry and adopt.

With 96% of ballots counted, 370,000 people had voted down the proposal, or 63.21%, surpassing the 342,000-minimum threshold to throw it out.

In order for the result to be valid, the winning side had to garner the support of at least 20% of the country's over 1.7 million registered voters. 

Opponents, disapproving in particular of the legislation giving gay couples the right to adopt, had mobilised to force a popular vote on the issue.

Pope Francis last week urged a 'no' vote as he called on the largely Catholic country to "back the family as the structural reference point for the life of society". 

Parliament's approval of the bill last March had made Slovenia Europe's first former communist state to offer same-sex couples the right to marry in the nation of two million.

The parliamentary legislation had defined marriage as a "union of two" instead of a "union of a man and a woman".

Following Sunday's vote, Slovenia's family code will revert to limiting marriage strictly to male and female couples after the referendum suspended the bill's application.

Both the country's president and prime minister had backed the 'yes' camp.