Germany's Social Democrats narrowly won Sunday's national election, projected results showed, and claimed a "clear mandate" to lead a government for the first time since 2005 and to end 16 years of conservative-led rule under Angela Merkel.

The centre-left Social Democrats (SPD) were on track for 26 percent of the vote, ahead of 24.5 percent for Merkel's CDU/CSU conservative bloc, projections for broadcaster ZDF showed, but both groups believed they could lead the next government.

With neither major bloc commanding a majority, and both reluctant to repeat their awkward "grand coalition" of the past four years, the most likely outcome is...