German voters looked set to hand Angela Merkel a third term in the first national election since Europe's debt crisis erupted four years ago.
But voters may force her into a coalition with her leftist rivals and introduce a new anti-euro party into parliament.
Reuters reports the most recent opinion polls show support for Mrs Merkel's conservative block, the Christian Democratic Union and the Bavarian Christian Social Union - at around 39%.
This is some 13 points ahead of the centre-left Social Democrats (SPD), the second-biggest party.
That virtually guarantees that Mrs Merkel will stay on as chancellor.
But her current partner, the business-friendly Free Democrats, has seen its support slide and she may be forced to court the SPD.
The wild card in the election is the Alternative for Germany, a new party that has seized on voter fears about the cost of euro zone bailouts, for which Germany underwrites the biggest share.
Polling stations opened at 8am on Sunday and the first exit polls were to be published at 6pm.
Of the 62 million Germans eligible to vote, about a third described themselves in the run-up to the election as undecided, adding to the uncertainty.