Marki-Zay, a small-town mayor and Catholic father of seven, who leads a six-party opposition alliance against Prime Minister Viktor Orban, also told supporters that a government under his leadership would draw up a new constitution and seek to have it approved in a referendum.

For the first time since 2010, Orban and his ruling nationalist Fidesz party will face a united front of opposition parties in this election.

Orban's path to re-election is also complicated by surging inflation and a row with the European Union over democratic standards, which has triggered a freeze in pandemic recovery funding.

Marki-Zay said Orban's "unlimited power has resulted in unlimited corruption", while millions of Hungarians were struggling to make ends meet. Headline inflation ran at an annual 7.9% in January.

"A few people have amassed unlimited wealth for themselves and their friends... We can see the yachts, private jets and villas," he said in a speech.

Marki-Zay said a government led by him would set up an anti-corruption agency to root out corruption, raise wages, introduce the euro and double child-linked family subsidies.

Marki-Zay said his government would keep in place the fence Orban had built on the border with Serbia in 2015 to keep out migrants.

The opposition alliance includes the Democratic Coalition, the Socialists, liberals and the formerly far-right, and now centre-right, Jobbik.

Orban's ruling Fidesz party gained a two-point lead this month over the opposition according to an opinion poll by Zavecz Research published on Monday.

To soften the impact of surging prices, Orban placed curbs on the cost of basic foods in February and extended caps already in place on the price of energy, fuel and mortgage borrowing.