The centre-right European People's Party (EPP) has won the most seats in the European Parliament, but eurosceptic parties have made strong gains, officials have said.
The EPP won 178 seats, just ahead of the 152 won by traditional centre-left rival the Socialists and Democrats, but various populist, eurosceptic and right-wing parties won more than 100 seats, parliament spokesman Jaume Duch told reporters.
France's Emmanuel Macron, who has staked his presidency on persuading Europeans that the EU is the answer to the challenges of an uncertain, globalising world economy, took a personal hit when his centrist movement was edged into second place by Marine Le Pen's anti-immigration, anti-Brussels National Rally.
But Mr Macron's Renaissance, built on the ruins of centre-left and centre-right parties, added to gains for liberals at the EU level.
Along with a surge for the Greens, that meant four groups occupying the pro-EU middle ground lost under 20 seats, securing 505 seats out of 751, according to a projection by the European Parliament.
That may complicate some policymaking, as a two-party "grand coalition" of the conservative European People's Party (EPP) and the Socialists (S&D) no longer has a majority.
The liberals, with 100 seats, and Greens, with 70, will want a big say.
But it also dents the hopes of Ms Le Pen, Italian Deputy Prime Minister Matteo Salvini and others who have been seeking to disrupt attempts to forge closer EU integration.
Tensions among nationalists, who also include the Polish and Hungarian ruling parties and the new Brexit Party of British campaigner Nigel Farage, have limited their impact on policy.
Luxembourg's liberal Prime Minister Xavier Bettel tweeted: "Europe wins! Voter turnout very high and pro-European parties are strongest."
EU officials were delighted by an increase in turnout to 51%, up from 43% in 2014. It was the first reverse in a trend of falling participation since the first direct EU vote in 1979.
At its highest in 20 years, that turnout may muffle talk of a "democratic deficit" undermining the legitimacy of EU lawmaking.
In Germany, Chancellor Angela Merkel's conservatives lost seven percentage points from five years ago as the far-right Alternative for Germany gained four points to 11%.
But the headlines there went to the Greens, who nearly doubled their vote to finish second on 21%, ahead of the Social Democrats.
Britain voted on Thursday but began releasing partial results only late today. The BBC said Mr Farage's Brexit Party was set for a big win, reflecting frustration at the fact Britain is still in the EU, two months after Brexit was supposed to happen.
Mr Farage is determined that his MEPs will not sit for long in Brussels - though drama after the resignation of Prime Minister Theresa May leaves the fate of Brexit still very uncertain.
In France, an official in Macron's team acknowledged "some disappointment" that, with some 22%, the president's Renaissance movement had lost first place to Le Pen's National Rally, which exit polls put on 24%.
However, pro-EU parties were still in the majority, with the French Greens coming third.
Added to the dazzling second place of their German counterparts, that lent credibility to expectations of a "green wave" that will influence policy in Brussels in the coming years -promoting controls on industrial polluters of the air, seas and land and tightening terms for EU trade deals with others.
The Parliament's projection put the EPP on 178 seats, ahead of the S&D on 152, with the liberals on 108, up 39 seats, and Greens on 67, up 15. On the far-right, two groups in the current parliament had a combined 108 seats, a 40% gain from 2014.
The European Parliament election will usher in weeks and possibly months of hard bargaining over who will run EU institutions. Party spokespeople for the four pro-EU centre parties were quick to talk of plans for a broad coalition.
The Parliament as an institution has insisted that one of its own winning members should succeed Jean-Claude Juncker as president of the executive European Commission.
But many national leaders, who will meet over dinner in Brussels on Tuesday, have said they will not be bound by that demand.
Greece set to call snap elections following European votes
Greek Prime Minister Alexis Tsipras has said he will call for early polls next month after a drubbing at European and local elections.
"Following the second round of local elections (on 2 June), I will ask the president to immediately call national elections," Mr Tsipras said in a televised address.
A likely date for the ballot is 30 June, news reports said.
With about a third of polling stations accounted for, Mr Tsipras' leftist Syriza party scored less than 24% in the European ballot compared to more than 33% for the main opposition conservative party New Democracy.
And in local elections, early results showed New Democracy in control, or securing outright, the bulk of Greece's 13 regions.
"I will not run away or quit the struggle for equality, solidarity, social justice," said Mr Tsipras, Greece's youngest prime minister in 150 years and the first avowed atheist leader.
"The electoral result... is not worthy of our expectations," he said.
New Democracy leader Kyriakos Mitsotakis had earlier called on Alexis Tsipras to resign.
Mr Tsipras' four-year term was originally to run until the autumn.