Berlin voters are heading into one of the closest state elections in the German capital's history, with the conservative CDU, left-wing Die Linke, far-right AfD and Greens running neck and neck in the polls.

Housing affordability and rising rents are dominating the campaign, while security concerns have gained prominence following a recent attack on the city's Pride celebrations.

With coalition options wide open and mainstream parties ruling out cooperation with the AfD, the outcome could reshape Berlin's political landscape and determine who governs Germany's largest city.