Referendum : Results expected to arrive between 8pm and 10pm
She said 8,272,625 citizens are registered, so 4,136,313 people must cast a valid vote for the referendum to be valid, adding that more than half of those casting valid votes must give the same answer to the question for the referendum to be successful.
The number of voters with a Hungarian residence is 7,997,998, 11,231 of whom will vote at one of Hungary's embassies abroad while 80,005 are registered to vote at a location in Hungary other than their residence. Many people not resident in Budapest are registered to vote in the capital, which could result in queues, especially in the 11th district, Palffy said.
A further 274,627 voters are ethnic Hungarians not resident in Hungary, and they can cast their vote by mail.
The biggest polling stations abroad are in London, Munich, Miercurea Ciuc (Romania) and Brussels.
Twenty-three international observers have been registered for the Sunday referendum, according to data on the NVI's website.
Twelve observers are delegated by the embassies of Mongolia, Denmark, the United Kingdom, the United States and the Netherlands and a further eleven by Romania's, South Korea's and Latvia's national election committees.
About 121,000 postal votes have already been cast, according to the calculations of the National Election Committee, Ilona Palffy said on Saturday, of which more than 88,000 have already arrived at the NVI.
Voting has already started at Hungarian embassies on the American continent, with polling stations first opening in Brazil, Chile and Argentina, then in Canada, Washington and New York. Cuba is followed an hour later by Chicago, Mexico City and Quito, capital of Ecuador. Voting on the American continent will close at 4am CET in Los Angeles.
Ilona Palffy said there is no campaign silence in Hungary on Sunday, apart from within a distance of 150m from polling stations, but no election rallies are allowed.
She said accusations of election fraud were "outrageous and unacceptable", and she rejected the allegations on behalf of the about 50,000 members of ballot counting committees. She said there are 10,331 such committees operating at the referendum, all with at least five members. All parliamentary parties had the opportunity to delegate members to each of the committees. Fidesz delegated 13,880 members, Jobbik 175, KDNP 279, LMP 41, and MSZP 4,012 members to ballot-counting committees.
In the referendum Hungarian citizens will be asked: "Do you want to allow the European Union to mandate the resettlement of non-Hungarian citizens to Hungary without the approval of the National Assembly?"