Prime Minister Viktor Orban told tens of thousands of supporters gathered in Budapest on Thursday that Hungary's "way of life will lose its meaning" if his opponents win the upcoming parliamentary election.
Orban told the rally, a show of strength ahead of the April 8 vote, that his enemies "want to take our country away from us", painting himself as the defender of "millions with national feeling" against the "globalist elite".
He repeated his key campaign themes in attacking international NGOs and US billionaire George Soros -- whom he accuses of meddling in Hungarian politics -- as well as his vehement opposition to immigration.
"They want others to live in this country," he told the crowd.
"Large western European countries bit by bit are losing their own countries, they want to force us to do the same, and this election is a great opportunity for them to do so."
"Africa wants to kick down our door, and Brussels is not defending us."
Another 10,000 people gathered in Budapest for a counter-demonstration, one of several such rallies planned during the day, according to an estimate by an AFP journalist at the scene.
A further 5,000 attended a leftwing rally organised by the socialist MSZP party and former prime minister Ferenc Gyurcsany's DK.
Polls put the 54-year-old Orban, who has repeatedly clashed with Brussels over immigration and the rule of law, firmly on course to win a third consecutive term.
But a surprise by-election defeat for Orban's ruling Fidesz party last month suggests the race may be tighter than expected.
Critics say the charismatic strongman has eroded democratic institutions like judicial independence and the media, and steered Hungary towards authoritarian one-party rule.
After he came to power in 2010, Orban placed loyalists in charge of state institutions and rewrote both the constitution and election rules, cementing his grip on power.
His second four-year term has been dominated by nationalistic and anti-immigration campaigns that detractors say have stoked xenophobia in the central European country of 10 million.
But bolstered by an improving economy and with the opposition divided, the former student leader of demonstrations that brought down communism nearly 30 years ago still enjoys strong support.
His supporters say Orban defends Hungary against meddling by the EU and Soros, and that his reforms are cleaning up a mess left by previous Socialist-led governments.
Numbers at the pro-Orban "Peace March" were swelled by people brought in from outside the capital and also from Poland, which has also clashed with Brussels.
At the front of the march was a banner reading "Homeland Before All", while others carried slogans saying: "God protect Hungary and Poland from leftwing ideology!"
"This government supports the Hungarian people by helping them start families," David Magyar, a 23-year-old economics student told AFP.
"We feel safe here," said a 53-year-old business woman, who gave her name only as Gyongyi.
"There isn't a single refugee running around the streets."