With a promise that the two key European partners would maintain their "essential cooperation," French President Emmanuel Macron late on Sunday led the praise for German Chancellor Angela Merkel as she secured a fourth term in office in Sunday's federal election.

"I called Angela Merkel to congratulate her. We will continue our essential cooperation with determination for Europe and for our countries," Macron told his followers on Twitter.

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Spain's Prime Minister Mariano Rajoy said Merkel's re-election would serve to promote "the European integration project."

In a telegram sent to the chancellery, Rajoy congratulated Merkel on the "excellent results," after her Christian Democrats (CDU) and their Bavarian sister party the Christian Social Union (CSU) scored a projected 33 percent of the vote, short of an outright majority.

Israeli Prime Minister Benjamin Netanyahu sent similar greetings, describing Merkel as "a true friend of Israel."

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AfD surge 'a shock'

In Brussels, the first European Union diplomat to comment on the election results was Pierre Moscovici, the commissioner for economic and financial affairs, who focused on the groundswell of support for the far-right populist Alternative for Germany (AfD) party. The AfD's projected 13 percent of the vote will see them enter the lower house of parliament for the first time.

Le Pen (right) congratulated the AfD and its chairwoman Frauke Petry (left)

"The AfD's entry into the Bundestag is a major shock and bluntly reveals doubts in society," Moscovici tweeted. But he added that "German post-war democracy is strong. No amalgam with 1933," in reference to the year Adolph Hitler's National Socialist party, the Nazis, seized power.

The leaders of Europe's other far-right parties were near the front of the line to congratulate their German counterparts.

"Bravo to our allies from AfD for this historic score! It's a new symbol of the awakening of the peoples of Europe," tweeted French National Front leader Marine Le Pen.

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Wilders jubilant

Rather than praising the AfD directly, Dutch far-right leader Geert Wilders ranked the popularity of each of Europe’s main anti-immigration parties in his tweet, shortly after the exit polls were released.

Highlighting how the AfD were projected to be the third-largest party in Germany and his own Dutch Party for Freedom, who was ranked number two in the Dutch election in April, he added: "The message is clear. We are no Islamic nations."

Meanwhile, the leader of Italy's populist Northern League party, Matteo Salvini, welcomed the AfD's surge, saying: "The desire for change is growing. It's up to us."

Unable to resist a dose of schadenfreude at Merkel's dip in support and the rise of the populists, former Greek Finance Minister Yanis Varoufakis hinted that the result of Sunday's election was linked to the role played by Germany's leaders in Greece's debt crisis.

“In 2015 Merkel & Gabriel crushed the Greek Spring together, while practicing socialism for bankers. Are they surprised now with the results?" said the economist, who resigned that year. He went on to say that the "CDU, CSU & SPD [Social Democrats] reaped the harvest they had sown."

Germany's SPD suffered its biggest loss of support since World War II, with a projected 20 percent of the vote, down more than 5 percentage points over the 2013 election.

mm/cmk (AP, AFP, EFE, Reuters)