Hungarians were voting Sunday in a referendum on the European Union's plan to settle migrants and refugees in their country according to quotas for the bloc's member countries.
Under a plan approved by a majority of EU member states last autumn, the bloc is aiming to resettle 160,000 asylum seekers stranded in Italy and Greece across the bloc, with 1,300 assigned to Hungary.
The "Yes" or "No" question on Hungary's ballot asks voters, "Do you want the European Union to be able, without consulting [the Hungarian] parliament, to decree the compulsory settlement of non-Hungarian citizens into Hungary?"
By 1 pm (1100 GMT), 23.6 per cent of the electorate had cast their votes, according to the electoral commission.
More than 8 million Hungarians are registered to vote, and a turnout of more than 50 per cent is required to make the referendum valid. Observers expect a turnout of 40-45 per cent.
Prime Minister Viktor Orban, fiercely anti-immigrant, has been vocal in his opposition to the EU relocation plan and even suggested recently that the more than 1 million people who arrived in the EU during the 2015-16 migration crisis should be expelled to "a large island."
Orban, speaking as he cast his vote in Budapest, said parliament would recognize the referendum results with a lower-than-required turnout.
"We will do it if the referendum is valid and also if it isn't," Orban said. "The only condition is that there must be more nos than yeses," Orban said.
It remained unclear what the legal repercussions of a "No" vote would be, with EU officials insisting that Budapest cannot reverse the decision on migrant quotas.
Polls close at 7 pm (1700 GMT) and results are expected late Sunday.
The head of the European Parliament criticized the referendum.
"Hungary would have to accept just some 1,300 refugees after the distribution key," Martin Schulz told the newspapers of Germany's Funke media group.
"To hold a referendum on it is a dangerous game," Schulz said. "[Orban] is questioning the legitimacy of the European legislative process, in which Hungary itself participates."
Last year Hungary was the first country to build a border barricade and ban migrants, including refugees, from entering its territory, with several other countries later following its example.
In December it also filed a legal challenge to the EU quota plan.