Germany votes Sunday in one of the most unpredictable elections in its recent history, with Angela Merkel's conservatives and the centre-left Social Democrats in a tight race for her crown as she prepares to leave the political stage.

The epochal election ushers in the end of 16 years in power for Merkel and places Germany, a byword for stability, in a new period of uncertainty.

Opinion polls show the race for the chancellery headed for a photo finish, with Merkel's CDU-CSU conservative alliance on around 23 percent, just behind the centre-left Social Democrats on 25 percent -- well within the margin of error.

"We will certainly see some surprises on Sunday," said Nico Siegel, head of the Infratest Dimap polling company.

Despite the SPD's lead in the polls, a victory for the conservatives "can't be ruled out", he said.

"The race for first place is wide open."

Around 40 percent of Germany's 60.4 million eligible voters have said they are undecided, while the same proportion have already cast their ballots by post -- including Merkel herself.

The battle for the chancellery has boiled down to a contest between two men: Finance Minister and Vice Chancellor Olaf Scholz, 63, of the SPD, and Armin Laschet, 60, of the CDU-CSU.

But with both parties likely to fall well short of the majority needed to govern alone, there could be weeks or even months of fraught coalition negotiations.

After Germany's last election in September 2017, it was February before the CDU-CSU formed a coalition with the SPD.

- Green wave that wasn't -

Laschet, an affable but gaffe-prone centrist and longtime Merkel ally, was for some time the clear favourite to take the reins after the veteran chancellor leaves the stage.

But his popularity began to wane after a series of blunders over the summer, including being caught on camera laughing in the background during a tribute to the victims of devastating floods in Germany.

In the meantime, Scholz, who at the start of the year had looked down and out in the race, saw his ratings begin to rise as he avoided making such embarrassing mistakes.

Often described as capable but boring, Scholz has positioned himself as a safe pair of hands and the true Merkel continuity candidate, despite hailing from a different party.

Along with social justice, climate change has been one of the top concerns among voters in the run-up to the election.

The Green party enjoyed a surge in support earlier this year after naming 40-year-old Annalena Baerbock as its chancellor candidate, at one point even briefly taking the lead as the most popular party.

But after a series of missteps by Baerbock, including a plagiarism scandal, the Greens are now polling well behind the two leading parties on around 17 percent.

While the chancellery may be out of reach for the party, it will likely have a role in Germany's next government.

- Partnership -

All bets are off on the composition of the next coalition, as the SPD and the conservatives could each try to cobble together a ruling majority if there is little to divide their score.

On the eve of the polls, Scholz voiced his preference for a partnership with the Greens, calling on voters to give him the score needed to go with a two-way coalition.

If those numbers don't add up, he may have to also rope in the liberal FDP, which is not a natural bedfellow with the SPD or the Greens.

Laschet has signalled he could still try to form a coalition even if the CDU-CSU do not come first, most likely calling on the FDP and the Greens for support.

But coming second would be a devastating blow for the party, which has dominated German politics since World War II and has never won less than 30 percent of the vote in federal elections.

What is at stake?

What will Germany look like after Angela Merkel's era and how will its role evolve in Europe and beyond?

Will the centre-left SPD manage to wrest power from the conservatives? Will the Greens or the liberals be part of the next government?

These are just some of the questions thrown up by Sunday's hotly contested election.

- Why is Merkel leaving? - 

Merkel, 67, announced that her current and fourth term in office would be "the last" in October 2018, when her CDU had just suffered a regional electoral setback.

The decision marks the first time since 1949 that an incumbent chancellor has not stood for re-election.

Appointed chancellor for the first time on November 22, 2005, Merkel has been in office almost as long as Helmut Kohl, Germany's longest-serving leader who was in power for just over 16 years (5,869 days). 

Under Merkel's leadership, Germany has been synonymous with stability in Europe. That could change after the election, with fragmented voting likely to result in a three-party coalition government.

- Could the conservatives lose power? -
The latest opinion polls have Merkel's CDU and the CSU, its Bavarian sister party, on around 22 percent -- which would be their worst election score in post-war Germany.

In the last election in 2017 under Merkel, the conservatives scored 32.8 percent.

If the polls are correct, the CDU-CSU risks losing the chancellery and may even be relegated to the opposition for the first time since 2005.

A year ago, experts had all but written off the possibility that the centre-left Social Democrats (SPD) would be part of the next government.

But they are now polling at about 25 percent and dreaming of fielding their first chancellor since Gerhard Schroeder.

- What happened to the far right? -
In 2017, the far-right Alternative for Germany (AfD) entered parliament for the first time as the largest opposition party after seizing on anger over Germany's 2015 refugee influx.

It appears to have lost support since then, currently polling at around 11 percent.

However, the party remains firmly rooted in Germany's political landscape and has most recently sought to court voters from the anti-mask movement, with members joining rallies against coronavirus measures.

- Who could be the kingmakers? -
The Greens, currently polling on around 17 percent, and the liberal FDP, on about 11 percent, could both find themselves being asked to prop up whichever party wins the election to form a government.

But an array of different coalitions are possible, ranging from a purely left-wing alliance to a predominantly right-leaning government.

Whatever happens, there are likely to be weeks or even months of fraught coalition negotiations -- leaving Europe's biggest economy withdrawn from the international scene for some time.

- What about foreign policy? -

Germany's foreign policy could look very different depending on who ends up in government.

Under a left-wing coalition including the SPD and the Greens, the country would be more inclined towards financial solidarity in Europe than it would be under the conservatives and liberals.

Tensions with NATO could emerge if the government includes the far-left Die Linke, which wants to abolish the transatlantic alliance.

The change of government could also affect the relationship between Germany and France, a partnership at the heart of the European Union -- especially with France also going to the polls in April 2022.

With a new team in place, the pressure will be on Germany to bring fresh momentum to EU policymaking, according to Paul Maurice, a member of the Franco-German Studies Committee at the French Institute of International Relations.