Europeans have headed to the polls in their tens of millions today as 21 countries choose their champions in a battle between the nationalist right and pro-EU forces to chart a course for the union.

Turnout by midday was higher than it had been in 2014 in some countries, notably France and Romania, and roughly stable in others, as reports began to trickle in from around the continent.

Each previous EU election since the first in 1979 has seen turnout fall, but initial figures from across the 28-nation bloc suggested this year's culture clash has mobilised both populists and those who oppose them. 

"I guess that some marginal parties will be less marginal tonight," European Commission president  Jean-Claude Juncker said as he cast his vote in his native Luxembourg. 

In the Polish seaport of Sopot, European Council chief Donald Tusk expressed confidence that voters would not back what he called "radical political movements, eurosceptics".

"The first priority, not only for this institution, is to save the EU as a project, not only at this time but in the long term, and I'm sure that they will manage,"  he told reporters.

Seven EU member states had already voted, but no official results can be published until rest have taken part. 

Eurosceptic parties opposed to the project of ever closer union hope to capture as many as a third of the seats in the 751-member Strasbourg assembly, disrupting the pro-integration consensus.

The far-right parties of Italian deputy PM Matteo Salvini and France's Marine Le Pen will lead this charge, and anti-EU ranks will be swelled by the Brexit Party of British populist Nigel Farage.

France's President Emmanuel Macron has taken it upon himself to act as figurehead for the centrist and liberal parties hoping to shut the nationalists out of key EU jobs and decision-making.

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"Once again Macron is daring us to challenge him. Well let's take him at his word: On 26 May, we'll challenge him in the voting booth," Ms Le Pen told a rally on Friday.

It was not clear at midday which side was carrying the day, but the battle seems to have motivated French voters, with 19.26% turning out, 3.5 points up from the same point in 2014.

Election campaign billboards in Berlin 

Meanwhile, the mainstream parties are vying between themselves for influence over the choice of a new generation of top EU officials, including the powerful president of the European Commission.

And turnout will be closely scrutinised in case another drop in participation undermines the credibility of the EU parliament as it seeks to establish its authority.

Britain and the Netherlands were first to vote, on Thursday, followed by Ireland and the Czech Republic on Friday with Slovakia, Malta and Latvia yesterday, leaving the bulk of the 400 million eligible voters to join in today.

At the last EU election in 2014, Slovakia had the lowest turnout of any country, at less than 14%, and centrist president Andrej Kiska is worried that "extremists are mobilising".

Spain is holding local, regional and European Parliament elections today

Poland's right-wing government, led by Law and Justice (PiS), has been accused of breaking European law by undermining the independence of the judiciary, but Polish voters still say they support EU membership.

"I would like there to be no nationalists in the parliament, or at least that they do not have a majority," retiree Ryszard Dabrowski told AFP at a Warsaw polling station.

But the right and the far-right have not had everything their own way so far.

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In the Netherlands, the centre-left party of EU vice president Frans Timmermans won the most votes and added two seats for the Socialists and Democrats in parliament, according to exit polls.

The S&D's centre-right rival - the European People's Party (EPP) - was buoyed by exit polls suggesting that Taoiseach Leo Varadkar's pro-EU Fine Gael party was in the lead in Ireland.

Even if Britain leaves the European Union on 31 October, the latest deadline for Brexit, then its MEPs could still play a role in this summer's scramble to hand out top jobs.

Thursday's votes from Britain won't be counted until after polls close in Italy, but Nigel Farage's Brexit Party appears on course to send a large delegation to a parliament it wants to abolish.

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Macron and the EU world beyond Brexit

Emmanuel Macron is pinning his hopes on his Renaissance movement joining with the liberal ALDE voting bloc and other centrist groups to give impetus to his plans for deeper EU integration.

But much will depend on who gets the top jobs: the presidencies of the Council and the Commission, the speaker of parliament, the high representative for foreign policy and director of the European Central Bank.

EU leaders have been invited to a summit dinner on Tuesday to decide how to choose the nominees, and Germany's Chancellor Angela Merkel is expected to back the lead EPP candidate Manfred Weber for the Commission.

French President Macron and some others oppose both Mr Weber, a German conservative MEP with no executive experience, and the idea that the parliament should get to choose one of its own for Brussels' prime post.

Whichever way the leaders lean, there will be no immediate decision. Instead, Council president Donald Tusk will take note of how the debate went and draft the nominations before a 21 June EU summit.