Turnout was 44 percent, with only 40 percent casting a valid vote. Of those who did vote, 98 percent of people supported Orban's call to prevent the EU from obliging Hungary to take in refugees.

The European Commission said Monday "it takes note" of the outcome of the referendum.

"We respect the democratic will of the Hungarian people, both of those who voted and those who did not," commission spokesman Margaritis Schinas told journalists.

"It is for the Hungarian government to decide how to deal with the outcome of this referendum," he added.

'In the spirit of'

Despite the invalid plebiscite, Hungary's prime minister Viktor Orban said he would make a constitutional change on immigration "in the spirit of the referendum."

He did not give details on the upcoming legislation.

"Sunday's referendum has achieved its goal," Orban said in parliament on Monday, highlighting that over 3.2 million voters rejected the EU mandatory quota idea - more than the number of people who voted in 2003 in favour of Hungary joining the EU.

He said Hungary is the only EU member state, where voters were asked about the migration policy, that he said, could decide the EU's existence.

Orban went on to say the referendum's outcome does not result in a legally binding legislation for the Hungarian parliament, but he proposed to change the consitution to accomodate the vote's results.

"This decision, this support [from the voters] obliges me to act," Orban told parliament.

Opposition lawmakers booed, and some called for Orban's resignation.

Far-right Jobbik leader Gabor Vona said Orban has failed. "You will not be taken seriously by Brussels bureaucrats," he told parliament, adding that "Brussels will exploit your irresponsibility and mistake."

The Hungarian PM admitted he expects a tough fight in Brussels over the migration policy.

"The political elite and the supporters - also in Hungary - of unlimited migration and resettlement have a strong tool kit, they are loud, anti-democratic and violent," he told MPs.

Momentum suffers?

Analysts agree that Orban has suffered a blow, but it is far from politically fatal.

Csaba Toth at the Budapest-based Republikon Institute told this website Orban was not shaken by the vote, and the effect of the invalid referendum would be limited in Europe.

"It is a failure, but not a big failure for Orban," said Toth, who added that populist movements across Europe suffered a relative setback with the vote.

Fabian Zuleeg of the Brussels-based European Policy Centre, warned that we should not underestimate the referendum despite the low turnout.

"The [quota] issue is not going to go away, and Orban has no intention of toning down his rhetoric," he told this website, but warned that the fight against populism would be a long process, and ultimately a task for domestic politicians.