The two candidates running neck-and-neck to replace Angela Merkel as German chancellor called for a stronger European Union on Thursday, in a final TV debate that did little to shake up a race expected to end in lengthy coalition negotiations.

With days to go before the general election on Sunday that will see Merkel step aside after 16 years in power, her conservative CDU-CSU alliance is playing catch-up with the centre-left Social Democrats (SPD) in the polls, narrowing the gap to just two percent.

The vote is being closely watched by Western allies, wary of an uncertain outcome that could blunt the participation of Europe's biggest power on the international scene for weeks, if not months.

Foreign policy has featured little during the tight campaign, but in their final joint TV appearance, the two main contenders for Merkel's job -- Finance Minister and Vice-Chancellor Olaf Scholz from the SPD and Armin Laschet from Merkel's conservative bloc each called for a strong, sovereign Europe.

Angela Merkel: 16 years in power
Angela Merkel: 16 years in power AFP / Sophie RAMIS

"We need more Europe, we need to speak with one voice," said Laschet, who is also the premier of North Rhine-Westphalia state.

"So we can act even when the US pulls back," he said, in a nod to America's chaotic exit from Afghanistan.

Scholz said the EU needed to stick together to stay relevant on the global stage, and stressed the importance of cooperation with the United States and NATO.

Annalena Baerbock, the Green party's candidate for chancellor, called for a joint EU policy on China "so we're not played off against each other", advocating a combination of "dialogue" and "toughness" with Beijing.

Finance Minister Olaf Scholz has emerged as a 'capable but boring' heir to Merkel
Finance Minister Olaf Scholz has emerged as a 'capable but boring' heir to Merkel AFP / INA FASSBENDER

On domestic issues, the candidates repeated their usual talking points, likely doing little to sway undecided voters and leaving media commentators exasperated.

"Desperately seeking a winner!" the top-selling Bild wrote.

Latest opinion polls put Scholz's SPD in front at 25 percent, followed by the CDU-CSU at 23 percent, within the margin of error.

The CDU is portraying Armin Laschet (right) as the candidate to ensure continuity and cement Merkel's legacy
The CDU is portraying Armin Laschet (right) as the candidate to ensure continuity and cement Merkel's legacy AFP / John MACDOUGALL

The Greens are in third place at around 16 percent support, giving them a realistic chance of becoming a junior coalition partner in the next government.

If the surveys prove right, Merkel's conservatives are headed for their worst score in post-war German history, potentially tarnishing Merkel's own legacy.

Their pick for chancellor, the affable but gaffe-prone Laschet, 60, saw his popularity decline after he was caught chuckling during a tribute to victims of deadly floods in July.

Often described as capable but boring, his centre-left rival Scholz came from behind to take the lead, casting himself as a safe pair of hands and the true Merkel heir.

The Greens' Annalena Baerbock is set to play "kingmaker" as Germany's polls predict a knife-edge contest
The Greens' Annalena Baerbock is set to play "kingmaker" as Germany's polls predict a knife-edge contest AFP / John MACDOUGALL

Climate change has emerged as a top concern among the 60.4 million people eligible to vote, including about 2.8 million able to do so for the first time.

Baerbock, 40, has warned that the next government "will be the last that can still actively influence the climate crisis".

Huge crowds are set to take to the streets on Friday as part of a global climate demo, with Fridays for Future founder Greta Thunberg coming to march in Berlin.

After steering Germany safely through crises such as the 2009-10 eurozone financial crunch, a massive influx of refugees in 2015 and the coronavirus pandemic, Merkel leaves behind an economic powerhouse in relatively robust health.

But critics say years of under-investment in infrastructure and education have left the EU's most populous country of 83 million people unprepared for a greener and more digital future, while social inequality has worsened.

Scholz and Baerbock have vowed more public investment to help the economy adapt, and higher taxes for top earners.

Laschet has argued that tax hikes could stifle the pandemic rebound and has pledged to cut red tape for businesses.

The unpredictable election is expected to yield a number of coalition options.

Laschet has already said that even if he comes second, he will try to cobble together an alliance with the Greens and the pro-business FDP.

The Greens have signalled they are more comfortable governing with the SPD.

Should they require a third partner for a parliamentary majority, the far-left Linke could step in, but their anti-NATO stance makes them a controversial choice.

A three-way marriage between the SPD, Greens and FDP is also possible.

None of the parties will partner with the far-right Alternative for Germany (AfD).

Coalition talks are likely to drag on for weeks, possibly months, keeping Merkel in office for a little longer.