BERLIN (AP) - Germany's political parties prepared to rally their supporters and win over undecided voters Friday, two days before a national election that will determine who succeeds Chancellor Angela Merkel after 16 years in power.

Merkel's center-right Union bloc, with Armin Laschet as its candidate for chancellorship, has made small gains in the polls in recent weeks. But it remains narrowly behind the center-left Social Democrats, headed by Finance Minister Olaf Scholz.

The Greens, who are putting forward their own candidate for chancellor for the first time, are trailing in third place, but could play kingmakers when it comes to forming a government.

Experts say one reason why this year's German election is tighter and less predictable than usual is that the candidates are relative unknowns to most voters.

“It's certainly not the most boring election,” said Hendrik Traeger, a political scientist at the University of Leipzig. “There were those in which Angela Merkel stood as the incumbent and it was simply a question of who she would govern with.”

This time, Merkel's party has struggled to energize its traditional base, which has so far failed to warm to Laschet, the governor of North Rhine-Westphalia state.

“The key question is whether these voters will overcome the Laschet hurdle and vote for the Union despite Laschet” said Peter Matuschek of the polling company Forsa. “Or will they abstain from the vote or even choose another party.”

The Union bloc will have its last big rally in Munich, while the Social Democrats are holding an event in the western city of Cologne. The Greens will stage their rally in nearby Duesseldorf.

Climate change has been cited as the most important issue by many in this election. Youth groups plan to stage a large protest outside the chancellery Friday to demand tougher action on climate change.

The economy and the fallout from the coronavirus pandemic have also played an important role during the campaign, while migration has is less of a concern to many voters than in 2017.

Foreign policy - largely absent from the campaign - became an issue during the final television debate Thursday, with the Greens calling for a tougher stance on China.

About 60.4 million Germans are eligible to vote for a new parliament on Sept. 26. The strongest party will seek to form a governing coalition.

The business-friendly Free Democrats are angling for a place in government this time, after pulling the plug on coalition talks at the last minute after the 2017 election. The far-right Alternative for Germany is expected to do well in the east, but other parties refuse to work with them. The Left party remains a possible governing partner for the Greens and Social Democrats, a prospect that has drawn alarm from conservatives.

Election officials say many more people will vote by mail this year, due to the pandemic, but this is not expected to significantly affect the turnout.