Germans voted in a general election Sunday expected to hand Chancellor Angela Merkel a fourth term while the hard-right nationalist AfD party is tipped to make history by winning its first seats in the national parliament.
Surveys suggest Merkel's conservative CDU/CSU alliance has a double-digit lead over its nearest rivals, the centre-left Social Democratic Party (SPD) led by Martin Schulz.
Polling stations opened at 0600 GMT in Europe's top economy and will close at 1600 GMT.
With four other parties predicted to clear the five-percent bar to enter into the Bundestag, the highest number since the 1950s, it could take months of coalition wrangling before the next government takes shape.
Mainstream parties however have already ruled out talking to the anti-Islam, anti-immigration Alternative for Germany (AfD), which is polling at 11 to 13 percent and could emerge as Germany's third-strongest party.
Alarmed by the prospect of what Foreign Minister Sigmar Gabriel branded "real Nazis" entering the Bundestag for the first since the end of World War II, politicians used their final days of campaigning to urge voters to reject the rightwing populist AfD.
"This Alternative for Germany is no alternative. They are a shame for our nation," former European Parliament chief Schulz said at a rally on Friday.
The latest surveys put support for Merkel's conservative block at 34-36 percent, with the SPD trailing at 21-22 percent -- which would translate into a historic low for the party.
Despite bracing for a drubbing, Schulz was all smiles as he and his wife cast their ballot in his western hometown of Wuerselen.
Merkel, 63, whose campaign events were regularly disrupted by jeering AfD protesters, said at her final stump speech in the southern city of Munich that "the future of Germany will definitely not be built with whistles and hollers".
Observers say a strong showing by the AfD, which has capitalised on anger over the influx of a million migrants and refugees since 2015, will hit Germany like a bombshell.
"If the AfD becomes the leading opposition party, they will challenge key themes," said Thorsten Benner, director of the Global Public Policy Institute in Berlin. "It will very much change the tone of debate in parliament."