The Fidesz-led coalition is projected to secure a majority to give Orban a 3rd consecutive term.
Orbán has leaned farther to the right in recent years, becoming one of Europe's most prominent populist voices. His critics said his stance has fueled xenophobia.
Since 400,000 people passed through Hungary in 2015 on their way to Western Europe, Orban has made migration the near-exclusive focus of his government.
This is the two-thirds control of the 199-seat legislature that allowed Fidesz to pass controversial laws putting pressure on the judiciary and the press.
Prime Minister Viktor Orban's Fidesz Party is enjoying wide support with its anti-immigration policy.
But as Chairman of the Party, Vona has gradually brought Jobbik into the mainstream in the hope of widening its political base.
'We are celebrating democracy and it seems like this feast will be lovely because many of us are taking part, ' said Gergely Karacsony, the leading candidate of the left-wing Socialist and Dialogue parties.
He has campaigned heavily on his unyielding anti-migration policies, although voters say they are more concerned with poverty, government corruption and the country's underfunded health care system.
Hungarian election officials say voter turnout in the country's parliamentary election 90 minutes before polls close has already exceeded the total turnout for the 2014 elections.
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A poll on Friday put Fidesz on 46% among decided voters, more than 20 points ahead of their nearest rivals Jobbik, on 19%.
"Unfortunately, for those on the right who are disappointed with Orban, there is no democratic conservative alternative like Germany's CDU or a French Macron-type party", said Paul Lendvai, a journalist and author of "Orban: Hungary's Strongman".
After casting his vote in a wealthy district of Budapest, he said he would stand up for Hungary's interests and said Hungary was a loyal member of worldwide organizations.
"We love our country and we are fighting for our country", Orban said.
But he added that since all parties, including Fidesz, had mobilized intensively, it did not necessarily mean Orban was threatened with defeat.
Orban, who voted with his wife at a Budapest school near their home, told a crowd of reporters that he will "respect the decision" of the Hungarian voters.
And if migrants settle in Hungary, Orban claims Hungary's economic development will end, its support for rural areas will dwindle, women and girls will be "hunted down" and Budapest, the capital, will become "unrecognizable".
Asked whether he was fighting the EU he said: "The EU is not in Brussels". The EU is in Berlin, in Budapest, in Warsaw, in Prague and in Bucharest.