Angela Merkel's party early on Tuesday firmly backed Armin Laschet to be the conservative bloc's chancellor candidate at Germany's upcoming elections, hoping to draw a line under a bitter battle with challenger Markus Soeder.

After more than six hours of talks, 46 executive board members of the Christian Democratic Union (CDU) held a secret online ballot that resulted in 77.5 percent support for party leader Laschet, participants told AFP.

Bavarian premier Soeder, leader of the CDU's smaller CSU sister party, garnered 22.5 percent.

Soeder, who is more popular than Laschet in opinion surveys, had earlier said he would accept the CDU's decision and step aside "without resentment" if senior members favored his rival.

The late-night vote marked the culmination of a bruising week-long power struggle that has brought Merkel's once stable CDU-CSU alliance to the brink of implosion.

With just five months to go before the September 26 election, when Merk el bows out after 16 years in power, the conservatives' poll ratings have plummeted recently over their handling of the coronavirus pandemic.

Laschet, a long-time Merkel ally and the premier of Germany's most populous state North Rhine-Westphalia, had already secured last weekthe backing of CDU top brass.

Elected as head of the CDU in January, Laschet would usually be the obvious choice to lead the center-right CDU and its Bavarian CSU partner into the elections.

But the 60-year-old has been panned in recent months for flip-flopping on measures aimed at curbing the virus spread in his state, even attracting criticism from Merkel herself.

Laschet's claim to be chancellor candidate has been fiercely contested by Soeder, 54, who after months of keeping Germans guessing about his ambitions finally announced his bid for the top job on April 11.

The former television journalist, who has echoed Merkel's stance for tough curbs to tame Germany's COVID-19 surge, currently commands more support from the German public and conservative lawmakers.

Merkel has not weighed in on the row, saying last week: "I wanted to, want to and will stay out of it."

A recent poll by public broadcaster ARD showed 44 percent of Germans thought Soeder most qualified to be the CDU-CSU's chancellor candidate. Laschet only had 15 percent of support.

Soeder told reporters on Monday that the CDU, as "the bigger sister party," had the ultimate say in who to send into the race for Merkel's job.

"We don't want to and we won't see a rift between the CSU and the CDU," he insisted.

It remains to be seen whether the CDU's internal vote marks the end of the conservative tug-of-war, with CDU-CSU parliamentarians set to hold a meeting on Tuesday.

The chaos in the conservative camp stands in stark contrast to the center-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.

Congratulating Baerbock on the nomination, Laschet promised a "fair election campaign" and urged parties to be "respectful" of each other in a veiled warning to Soeder.