Europeans vote on Sunday in an election expected to further dent traditional pro-EU parties and bolster the nationalist fringe in the European Parliament, putting a potential brake on collective action in economic and foreign policy.
Polls opened at 7 a.m. (0400 GMT) in the east of the bloc and will finally close at 11 p.m. (2100 GMT) in Italy. Seven states have already voted, with 21 joining in on Sunday in what is the world's biggest democratic exercise after India.
Right-wing populists top opinion polls in two of the big four member states - Italy and supposedly exiting Britain - and could also win in a third, France, rattling a pro-Union campaign championed by centrist President Emmanuel Macron.
However, exit polls in some countries that have already voted have given pro-EU parties some comfort. The Dutch Labour party, all but written off, looks to have finished first, helped by the visibility of having the EU socialists' lead candidate, current EU deputy chief executive Frans Timmermans, Reuters reported.
The Netherlands and the UK headed to the EU polls on Thursday — the first day of election — followed by Ireland and the Czech Republic on Friday and Latvia, Malta and Slovakia on Saturday.
A total of 420 million EU citizens are eligible to cast their ballot in these elections.
According to exit polls, the Netherlands' center-left party of EU Vice President Frans Timmermans won the most votes and added two seats to the Socialists and Democrats (S&D) bloc in the EU Parliament, Deutsche Welle reported.