In a Facebook post before the rally, organizers called for a recount of ballots, free media, a new election law, as well as more efficient cooperation among opposition parties instead of the bickering seen in the run-up to the vote.

The protest was among the biggest in Hungary in recent years, similar in size to a mass rally prompted by Orban’s plan to tax internet use four years ago and a pro-government demonstration called by Orban supporters shortly before the election.

There was a similar split between ages, with support for Orban’s Fidesz at 37 percent among voters below 30, rising gradually to 46 percent among those older than 50, according to a survey by think tank Median published earlier this week.

The Organisation for Security and Cooperation in Europe has said the election did not offer opposition parties a level playing field amid a host of problems marring a vote that nonetheless generally respected fundamental rights.

In their Facebook post, the rally’s organizers said: “Fidesz’s election system and the government’s hate campaign have pushed the majority into a one-third (parliamentary) minority.”

Protesters marched from the Opera House, a 19th century Neo-Renaissance palace on a majestic downtown avenue, to Parliament by the Danube River, waving Hungary’s tricolor flag and the European Union flag, accompanied by whistles and horns blaring.

As demonstrators filled a large square outside Parliament, many were still walking on main roads leading there, chanting: “We are the majority.”

“Viktor Orban has forgotten where he came from,” Ors Lanyi, one of the organizers told the crowd, which responded with loud boos upon hearing the prime minister’s name.

In contrast to Orban’s closing rally last week in his native Szekesfehervar, where the overwhelming majority of supporters were middle-aged and elderly people, the Budapest protest attracted many people from younger generations.

“We are disappointed and I think lots of us are disappointed with the election results, which, I think, were not clean,” said 26-year-old Palma, who declined to give her surname.

Palma, who came to the protest with a friend, said she believed the Hungarian election system gave an unfair advantage to Orban’s ruling Fidesz party. However, she was also displeased with opposition parties.

“They are pathetic,” she said. “It is terrible that they are so weak, unable to reach a compromise and they kill each other instead of joining forces for us.”

Nationalist Jobbik and the Socialists are the biggest opposition groups in parliament.

In the election campaign Orban projected himself as the defender of Hungary’s Christian culture against Muslim migration into Europe, an image which resonated with millions of voters, especially in rural areas.

But the opposition’s poor showing was at least partly of its own making as rival candidates split the anti-government vote in five districts in Budapest, where preliminary results showed a slim Fidesz victory.

“Zero, zero, zero,” 29-year-old Dia Szenasi said about the opposition, adding that all leftist parties should have joined forces to have a better chance of ousting Orban.