Hungarians voted Sunday on the EU's troubled refugee quota plan, in a referendum aimed at boosting Prime Minister Viktor Orban's self-styled campaign to defend Europe against the "threat of mass migration".

Polling stations close at 1700 GMT, with results expected later in the evening. By 12:00 pm (1100 GMT) turnout was just over 23 percent, according to the national election office.

"We are proud that we are the first to be able to vote on this question, unfortunately the only ones," Orban said after casting his ballot in the capital Budapest.

The firebrand leader has emerged as the populist standard-bearer of those opposed to German Chancellor Angela Merkel's "open-door" policy, in the wake of the bloc's worst migration crisis since 1945.

He has led a fierce media offensive urging the eight-million-strong electorate to spurn the EU deal, which wants to share migrants around the 28 member states via mandatory quotas without the consent of national parliaments.

Orban warned on Saturday that mass migration was a "threat... to Europe's safe way of life" and that Hungarians had "a duty" to fight the failed "liberal methods" of the "Brussels elite".