Dutch socialist Frans Timmermans looks like the big winner in the first exit poll from the 2019 European Parliament (EP) election.

Timmermans' centre-left Labour will unexpectedly emerge as the largest party in the EP vote, according to Dutch pollster Ipsos, which claims a margin of error of one seat.

Student or retired? Then this plan is for you.

Jean-Claude Juncker defended British prime minister Theresa May (Photo: European Commission)

It will win five of the 26 Dutch seats in the EU parliament, the pollster said.

Timmermans is a European Commission deputy who wants to succeed his boss, Jean-Claude Juncker, as its next president.

The win might give a bump to his candidacy.

"I hope that this gives a tailwind for a lot of other social democrats in Europe", he said in reaction on Thursday.

The Dutch exit poll, the first indicator of how the wider EP election might go, also showed most other pro-EU parties doing well.

Prime minister Mark Rutte's Liberals and the centre-right Christian Democrats shared second place, the poll said, with four seats each. The Greens got three.

The anti-EU newcomer Forum for Democracy party, led by Thierry Baudet, also won three seats, amid concern over a wider far-right surge in Europe.

The far-right National Rally party of Marine Le Pen in France will come first with 25 percent of the vote there on Sunday, according to a survey by pollster OpinionWay for newspaper Les Echos.

The liberal Republic On the Move party of French president Emmanuel Macron will come second with 23 percent, it said.

But in the Netherlands, one far-right party appeared to have cannibalised votes from another.

Baudet's party poached support from the anti-EU Party for Freedom, led by Geert Wilders, which plummeted from four seats to just one in its worst outcome in a decade.

The voter turnout was 41 percent, compared to 37 percent in 2014, with higher turnouts tending to favour mainstream candidates.

UK's 'Brexit' election

British voters also cast their ballots on Thursday (23 May) amid predictions that their prime minister is about to fall.

The anti-EU Brexit Party of Nigel Farage was, like Le Pen, polling to come top in the British EP vote.

But the UK result is being kept under wraps until Sunday evening, when all 28 EU states have finished voting.

Election day was quiet after an emotional build up, which included egg and milkshake throwing, as well as violence at one far-right EP campaign event.

It was marred by complaints by hundreds of EU nationals living in Britain that they were denied their right to vote due to bureaucratic errors.

They spoke out on social media under the hashtag #deniedmyvote. The3Million, an EU citizens' group in the UK, and some opposition Labour Party MPs and MEPs also called for an enquiry.

"I recognise that there is frustration," a British government spokesman said.

The British EP election took place under the shadow of Brexit, with Britain due to leave the EU on 31 October.

It also took place amid reports that British prime minster Theresa May will announce her resignation on Friday morning, plunging Britain deeper into political uncertainty.

May to resign?

George Osborne, a former finance minister in May's Conservative party who now runs the Evening Standard newspaper, said she would promise to go on 10 June after a state visit by US president Donald Trump and after a fourth and final vote on her EU withdrawal accord.

"May prepares to quit after cabinet mutiny," the Times newspaper's top story said.

"May set to go after Brexit fiasco," the mass-selling Sun newspaper said on its front page.

The expected resignation is to come after a senior cabinet member, Andrea Leadsom, quit in the run-up to the EP vote in protest that May had included the option of a second Brexit referendum in her latest version of the withdrawal bill.

If May is replaced by a hard Brexiteer, such as former foreign minister Boris Johnson, that could bode ill for future talks on an orderly EU exit.

For his part, Juncker, the outgoing EU commission president, defended May in an interview with US broadcaster CNN on Thursday.

"This is a woman who knows how to do things, but she is unable to succeed in doing things. I like her very much. She is a tough person," he said.

Juncker said he was "getting fed up" with British politics because "we [the EU] are [just] waiting for the next extension" of the Brexit deadline due to the UK's political instability.

"I would like to say yes to a second referendum, but the result might not be any different. We are observers in a British stadium - it's up to them to decide," Juncker added when asked if Brexit could still be stopped.