European Union leaders were quick to congratulate French President Emmanuel Macron on his election victory over his far-right rival on Sunday, reflecting relief that one of the bloc's most pivotal countries had avoided a political shock.

European Council President Charles Michel, as well as the prime ministers of Belgium and Luxembourg, were among the first to congratulate Macron, followed by almost all of the bloc's 27 leaders, after his win over Marine Le Pen by a comfortable margin.

"Bravo Emmanuel," Michel wrote on Twitter. "In this turbulent period, we need a solid Europe and a France totally committed to a more sovereign and more strategic European Union."

After Britain's surprise vote to quit the EU and the election of Donald Trump in the United States in 2016, the bloc was alarmed by Le Pen's potentially explosive social and economic reforms, even if polls showed Macron winning in Sunday's second round.

Britain's Prime Minister Boris Johnson, the public face of Brexit for many Europeans, applauded the result, pledging cooperation with Macron and saying that "France is one of our closest and most important allies."

France, a founding member of the EU, has been at the centre of efforts to integrate Europe since the end of World War Two, although such policies have been divisive. For all the sighs of relief, more than half of French voters supported candidates in the first round of the election who are critical of the EU.

Having Le Pen, a deeply eurosceptic politician who has professed admiration for Russian President Vladimir Putin, in the Elysee Palace would have had huge implications for the stability of the EU, analysts and diplomats said.

Le Pen had long flirted with the idea of leaving the bloc, although she insisted she had no "secret agenda" this time for quitting the EU or the euro single currency.

European Central Bank President Christine Lagarde, a French national, offered warm words for the pro-business Macron, saying "strong leadership is essential in these uncertain times."

The leaders of Sweden, Romania, Lithuania, Finland, the Netherlands and Greece, as well as European Commission President Ursula von der Leyen all reacted within about half an hour of the result with their congratulations.

"I look forward to continuing our extensive and constructive cooperation within the EU and NATO, and to further strengthening the excellent relationship between our countries," Dutch Prime Minister Mark Rutte said.

PRO-EU MOMENT 'MUST BE SEIZED'

Echoing the sentiment of many, German Finance Minister Christian Lindner said Europe was the biggest winner.

Italian Prime Minister Mario Draghi, who along with Macron and German Chancellor Olaf Scholz is seen as forming a powerful trio of pro-EU leaders, also said the re-election was "wonderful news for all of Europe."

Scholz offered continued Franco-German cooperation, which is regarded as the engine of European integration.

Many leaders referred to Macron as "cher (dear) Emmanuel".

The youthful centrist is one of the bloc's most pro-EU leaders, credited by many as having the vision to help it stand up to China's rise and Russia's military threat.

Spain's prime minister, Pedro Sanchez, tweeted his congratulations to Macron. Sanchez on Thursday wrote a joint op-ed in French daily Le Monde with Portugal's Antonio Costa and Scholz criticising Le Pen and urging people to vote for Macron.

"The chance that there will be pro-European governments in France and Germany for at least the next four years must be seized," Anton Hofreiter, chairman of the Europe Committee in the German Bundestag, said.