The rightwing nationalist prime minister projected himself as a saviour of Hungary's Christian culture against Muslim migration into Europe, an image which resonated with millions of voters, especially in rural areas.

According to preliminary results with 85 per cent of votes counted, National Election Office data projected his Fidesz party to win 133 seats, a two-thirds majority in the 199-seat parliament.

The Nationalist Jobbik party was projected to win 26 seats, while the Socialists were projected as third with 20 lawmakers.

The victory could embolden Orban to put more muscle into a Central European alliance against the European Union's migration policies.

Orban, Hungary's longest-serving post-communist premier, opposes deeper integration of the bloc and - teaming up with Poland - has been a fierce critique of Brussels' policies.

With his firm grip on state media and his business allies in control of regional newspapers, Orban's message was amplified in the countryside. There, many people only watch the state television news channel, which has showed immigrants causing trouble in western European cities night after night.

Critics say Orban has put Hungary on an increasingly authoritarian path and his stance on immigration has fuelled xenophobia.

Orban's strong win could boost other right-wing nationalists in Central Europe, in Poland and in neighbouring Austria, and expose cracks in the 28-nation EU.

The EU has struggled to respond as Orban's government has, in the view of its critics, used its two landslide victories in 2010 and 2014 to erode democratic checks and balances. It has curbed the powers of the constitutional court, increased control of the media and appointed loyalists to key positions.

Australian Associated Press