BERLIN, Sept 14 (Reuters) - Germany"s federal election is too close to call as the number of still undecided voters hit a record high less than two weeks before the poll, in which centre-right Chancellor Angela Merkel is not seeking a fifth term, a survey showed on Tuesday. The survey by the Allensbach research institute for the conservative newspaper Frankfurter Allgemeine Zeitung found that only 60% of voters who are determined to participate in the election have yet decided which party they will support. This means that 40% of the voters are still undecided, up from 35% at this point of the election campaign in 2017 and from just 24% in 2013. As the most important reason for their indecision, roughly two out of three respondents said none of the top candidates running to replace Merkel as chancellor was convincing. Some respondents also said their indecision stemmed from the fact that a lot can still happen before election day. Others said they were unsure how the party they were inclined to support might behave in future coalition talks. A Forsa poll for RTL/n-tv televison published on Tuesday showed Merkel"s conservatives with their top candidate Armin Laschet had gained two percentage points on the week to reach 21%. But the centre-left Social Democrats and their top candidate Olaf Scholz, current vice chancellor and finance minister, remained in pole position with a stable 25%. The Greens stood at 17%, the business-friendly Free Democrats (FDP) at 11%, the far-right AfD at 11% and the far-left Linke at 6%. This means that Scholz could become chancellor in a three-way coalition either with the Greens and FDP, also known as a "traffic light" coalition, or a more left-leaning alliance with the Greens and the Linke. But Laschet could, theoretically, also try to form a three-way coalition with the FDP and the Greens. All parties have ruled out working with the far-right AfD.