As September 24 nears, German Chancellor Angela Merkel's Christian Democrats (CDU) and their Bavarian sister party, the Christian Social Union (CSU), are polling a comfortable 17 percentage points ahead of would-be challengers, the Social Democrats.

In the latest Deutschlandtrend poll published Thursday, the Union of CDU/CSU held steady at 37 percent to remain the strongest party. In contrast, the SPD under Martin Schulz slipped to 20 percent, making it the party's worst result since January.

Read more: German election: What do the terms 'right' and 'left' mean, if both CDU and SPD are in the center?

It's also well below the 23 percent of votes the SPD got in the 2009 election, which marked their lowest ever Bundestag result.

Comparing people's preferred chancellor if it were a direct public vote, 51 percent would vote for Merkel, while only 25 percent favored Schulz. With fewer than two weeks to go until the election, only 57 percent of voters had decided which party they supported.

AfD a clear third place

The anti-immigration Alternative for Germany (AfD) party led the race for third place, with 12 percent of the vote, increasing its share slightly in comparison with last month's poll and meaning it's likely to enter the Bundestag for the first time. The AfD is already represented in 13 of Germany's 16 state parliaments.

Read more: AfD, on course for parliament, says Germany done with Nazi past

The Infratest dimap survey of 1,000 voters for ARD Deutschlandtrend was conducted by telephone on September 12 and 13.

The other smaller parties recorded minor differences compared to previous polls. The business-friendly Free Democrats (FDP) look set to re-enter the Bundestag with 9.5 percent of the vote. The Left and Green parties recorded slight losses, with 9 and 7.5 percent respectively.

All other parties combined recorded 5 percent of the vote.

Coalition preferences

If CDU/CSU voters could pick a coalition partner, almost half of them would choose the FDP. However, based on current poll results, that would not be enough to give them a majority in parliament. That would only be possible with another grand coalition of the CDU/CSU and SPD. Under these circumstances, there is no clear preference – 45 percent favored a grand coalition, while 46 percent supported a coalition between the CDU/CSU, FDP and the Greens. 

Read more: German election: Can the Greens and FDP join Angela Merkel in a coalition?

During the election campaign, the Social Democrats' candidate for chancellor, Martin Schulz, said he did not want to continue the status quo as a junior partner in a grand coalition. Of the SPD supporters surveyed, half preferred the SPD to be in government with the CDU/CSU again, while 46 percent would rather see them in opposition. The FDP supporters favored a coalition with the CDU/CSU. Of the Greens supporters, two-thirds said being part of a governing coalition would be more desirable than another term in opposition.