A total of 62.2 million people are eligible to vote in these national elections in Germany, Europe's biggest economy and most populous state.
Chancellor Angela Merkel's center-right Christian Democrats were the favorite heading into polling.
But opinion polls suggested they might no longer have enough support to be able to ditch their current coalition partners, the center-left Social Democrats, led by current foreign minister, Frank-Walter Steinmeier.
The two parties have shared power since the last election in 2005.
Merkel had hoped that her Christian Democrats would be able to form a center-right coalition with the business friendly Free Democrats that could push through economic reforms.
In a speech to supporters in Berlin on September 26, Merkel said her party was "fighting for the German jobs of the future" amid "the most serious economic crisis Germany has seen in the last 60 years."
Abroad, Merkel's main challenge is Afghanistan, where Germany has around 4,200 troops in the NATO-led forces.
The German public had become increasingly weary of Berlin's already seven-year long mission based in northern Afghanistan's Konduz Province.
The initial results could prove unclear due to Germany's complex electoral arithmetic.
Germany's electoral system is complex, with voters casting two votes on a single ballot paper. In the first vote, they choose a candidate in their district to the Bundestag, the lower house of parliament, and the winner takes up the district's seat. In the second vote, voters choose a party from some 29 parties participating in the election. Parties are awarded a certain number of seats per state depending on the proportion of votes they receive.
Security was tight after a series of Al-Qaeda videos in the past week warning Germany to pull out its troops of Afghanistan. The video threatens a "rude awakening" for Germany if voters back a government that supports keeping forces in Afghanistan.
All flights have been banned over the traditional Oktoberfest in Munich, and armed police were guarding airports, train stations, and city centers across the country.
compiled from agency reports