The ruling Fidesz party has received almost half of the 80% votes counted so far. Turnout is reported to be high.
The party is also tipped to keep its key two-thirds majority in parliament.
The campaign was dominated by immigration, with Mr Orban promising to defend the country’s borders and block migration by Muslims.
Mr Orban has already declared victory, telling ecstatic supporters that “high turnout has cast aside all doubts”.
The 54-year-old went on to say the result was an opportunity to defend Hungary.
Jobbik take second
Fidesz had been widely expected to win, but there have been doubts over whether it could retain its “supermajority” – a two-thirds control of the 199-seat parliament, which allowed it to pass controversial laws putting pressure on the judiciary and the press.
However the National Election Office data projected Fidesz as winning 134 seats, with the nationalist Jobbik party on 26 seats and the centre-left Socialists in third place with 20 lawmakers.
The BBC’s Nick Thorpe says that the Socialists and the Democratic Coalition appear to have done well in the capital Budapest. The formerly far-right, now moderate nationalist Jobbik party, however, appears to have failed to make major inroads into the Fidesz vote in the countryside.
Mr Orban – an avowed Eurosceptic – will likely seize on the results as vindication of his clashes with EU institutions over his tough anti-immigration measures and rejection of the EU’s refugee resettlement programme.
During his campaign, Mr Orban refused to publicly debate with his opponents or speak to the independent media, speaking instead at rallies for his supporters.
These addresses focused on one core policy – stopping immigration.
Under Mr Orban, Hungary built a fence along its borders with Serbia and Croatia in 2015 to stop illegal migrants. BBC
