Armin Laschet, the leader of Angela Merkel's party, on Tuesday urged her conservatives to unite in the run-up to September's elections, after he won their nomination as chancellor candidate in a bruising battle that pushed the bloc to the brink of implosion.

Laschet, 60, will lead Merkel's CDU and its CSU Bavarian sister party to the polls after his rival Markus Soeder conceded following a fierce challenge.

"We didn't make it easy for ourselves because in the end it is about a landmark decision in September for the future of our country," said Laschet, the premier of Germany's most populous state, North Rhine-Westphalia.

It was now important for the CDU-CSU alliance to "go into the election battle as a team," he said.

"The CDU won't win the election without the CSU and vice versa," he added, as Merkel led political leaders in sending congratulations for his nomination.

Laschet's challenger Soeder, who is head of the CSU, had earlier conceded the fight after the CDU's leadership came out in a late night vote for their incumbent party chief.

"There are days for discussion. There are days for decision. That has all happened and now it is important to look together into the future," he said, adding that he wished Laschet success and offered him the full backing of the CSU.

Soeder's climbdown came after nine days of backbiting among MPs and leading figures within the conservative bloc that left the once-stable alliance in disarray, just as Merkel is about to bow out from politics after 16 years in power.

While Laschet received the CDU's leadership's backing, 54-year-old Soeder commands far stronger support among the public.

A recent opinion poll commissioned by the Bild newspaper on Germany's most popular politicians even had Soeder topping the charts, just above Merkel, while Laschet languished in 12th place.

But Laschet, a sworn Merkel loyalist who famously backed the chancellor during the fallout from the 2015 refugee influx, has a history of coming back from behind.

Laschet, a long-time Merkel ally, had already secured the backing of CDU top brass last week Laschet, a long-time Merkel ally, had already secured the backing of CDU top brass last week Photo: AFP / Tobias SCHWARZ

Despite a souring mood at that time over the arrival of more than a million asylum seekers, Laschet seized North Rhine-Westphalia state -- a sprawling industrial region and a Social Democrat stronghold -- in a regional election in 2017, handing a major boost to the CDU.

A fluent French speaker and self-described "passionate European", he also prevailed in a battle for the CDU chief post in January, seeing off a fierce challenge from Friedrich Merz.

Yet he appeared to chart a course away from Merkel in March when he defied the chancellor's pleas for harder coronavirus shutdown measures from the leaders of Germany's 16 states.

Laschet defended North Rhine-Westphalia's broad interpretation of national virus measures, calling for "more freedom and flexibility".

With a recent poll by public broadcaster ARD showing 44 percent of Germans in favour of Soeder as most qualified as the CDU-CSU's chancellor candidate and Laschet only taking 15 percent, the 60-year-old will have his work cut out for him as he seeks Germany's top job.

In a reconciliatory gesture, Laschet promised that Soeder will "play a central role for the future of Germany".

After all, Laschet badly needs to reunite his troops behind him, something that senior CDU members have said could prove complicated.

After a late-night video conference on Monday when Laschet secured the backing of the CDU board, Volker Bouffier, regional premier of Hesse, warned the decision "may not be accepted" by the party rank and file.

The squabbles have damaged the alliance's standing at a time when Europe's biggest economy is struggling to end a pandemic that has killed 80,000 people and ravaged thousands of businesses and livelihoods.

The chaos in the conservative camp also stands in stark contrast to the centre-left Green party, polling second behind the CDU-CSU, which on Monday announced co-chair Annalena Baerbock as its chancellor candidate at a slick press event with no signs of strife.