Berlin - A sea change in German politics began this week with two leading parties announcing their candidates to succeed Angela Merkel at September's elections, when the veteran chancellor will bow out from politics.

After 16 years with Merkel at the helm of Europe's largest economy, politics in steady-as-it-goes Germany is entering a period of unpredictability.

A prelude of upheavals ahead came in the form of a damaging power struggle within Merkel's CDU-CSU alliance, that finally ended with Armin Laschet nominated as the conservatives' chancellor candidate.

Meanwhile, the opposition Greens have shot to the top of some surveys for the first time after they picked 40-year-old Annalena Baerbock as their chancellor candidate on Monday.

The race for Merkel's throne has now been blown wide open, heralding a dramatic shift in Germany's political landscape.

- Green Chancellor? -

Post-war Germany has been led only by chancellors from either the centre-right CDU party or the centre-left SPD party.

But with the Social Democrats polling only around 16 percent currently, there is little chance that they could make a comeback for Germany's top job with their chancellor candidate Olaf Scholz, Germany's current finance minister.

Rather, speculation is now rife that Europe's economic engine may well get its first Green chancellor come September.

A survey by Forsa on Tuesday showed Baerbock's Greens on 28 percent, an astonishing seven points ahead of the conservative CDU-CSU alliance.

Strong among younger and urban voters, the Greens have long since overtaken the social-democrats as Germany's second-biggest electoral force, and can now even dream of toppling the ruling conservatives.

At a regional level, the Greens are now part of government coalitions in more than half of Germany's 16 states, including in Baden-Wuerttemberg, homeground of auto giant Daimler.

Once notorious for their infighting, the ecologists presented a united front behind Baerbock -- something that has not gone unnoticed at a time when the CDU-CSU was in chaos over their own succession plans.

A former journalist and trained lawyer, Baerbock is considered strong on policy and detail but has no direct experience of government.

The Greens have however sought to draw comparisons with the likes of French President Emmanuel Macron and New Zealand Prime Minister Jacinda Ardern.

And Baerbock has presented herself as the candidate for renewal, saying that "others stand for the status quo".

- Squabbling conservatives -

While the Greens are basking in their latest popularity surge, Merkel's CDU-CSU alliance is struggling to pick up the pieces after bitter squabbles over Merkel's succession.

The conservatives finally plumped for Laschet on Tuesday after over a week of high drama that brought them to the brink of implosion.

Yet their subsequent slump in the polls to a record low of 21 percent appeared to confirm what many had feared -- that Laschet is too unpopular among voters to keep the conservatives in power.

According to Forsa, 63 percent of Germans think the CDU-CSU's chances are worse under Laschet than they would have been under his more charismatic Bavarian rival Markus Soeder.

"The CDU have lost their will for power," wrote conservative broadsheet Die Welt after Laschet's nomination.

Even before the damaging power struggle erupted, the conservatives were suffering in the polls because of the public's frustration over the government's handling of the pandemic.

Devastating accusations of corruption linked to mask procurement deals afflicting some of its lawmakers have also further hurt the conservatives' standing.

Laschet will therefore have his work cut out as he seeks to unify his troops behind him.

Critics warn that he will also have to draw up clear policy positions, weeks after other parties released their manifestos.

"Nobody knows what the conservatives stand for without Merkel as chancellor," wrote Der Spiegel weekly on Wednesday.

- Other constellations -

Much will now hang on whether Laschet manages to steady the conservative ship.

While most observers are still expecting a coalition of the Greens and the CDU-CSU bloc to emerge, a failure by the conservatives to stop a haemorrhage of support may well open the door to other possibilities.

A three-party left-wing coalition between the Greens, the Social Democrats and the radical Left party could well be possible.

Asked which would be her preferred coalition partner, Baerbock said her party is not interested in "tagging behind others".

"We would prefer to lead this government," she said.

By Kit Holden