Germany's left-leaning Social Democratic Party (SPD) has won the most seats in the country's federal election, preliminary results show, but it will be some time before the makeup of the new government is known.

The SPD claimed a narrow victory over the Christian Democratic Union (CDU), the centrist-right, the conservative party of outgoing Chancellor Angela Merkel, according to the "Federal Returning Officer" (Der Bundeswahlleiter) responsible for overseeing Federal elections.

The Federal Returning Officer website said the SPD won 25.7% of the vote, followed by the CDU/CSU bloc which garnered 24.1%, and the Green Party with 14.8% of votes, after a count of all 299 of Germany's "constituencies" or electoral districts.

The election ends Merkel's 16-year time in the top job, but her successor won't be decided until a coalition deal is negotiated.

The SPD will now begin negotiations to form the new government, a process that could take weeks -- or even months. After Merkel's election win in September 2017, it took more than five months for a government to be formed.

Though the preliminary count gives the SPD a small lead over its closest rivals, the results mark a significant improvement for the party that took 20.5% of the vote in the last election in 2017.

After exit polls on Sunday evening, both main candidates for chancellor, the SPD’s Olaf Scholz, and the CDU-CSU’s Armin Laschet, immediately claimed a mandate to govern.

Commenting after the exit polls, Laschet conceded the result was disappointing and said it posed a “big challenge” for Germany.

Signaling that another coalition with just the SPD was not probable, Laschet added that “it will probably be the first time that we will have a government with three partners.”