German Chancellor Angela Merkel attends a news conference after the EU summit in Brussels, Belgium, April 29, 2017. REUTERS/Christian Hartmann

BERLIN (Reuters) - German Chancellor Angela Merkel’s conservative Christian Democrats have opened a seven-point lead over the centre-left Social Democrats five months ahead of the Sept. 24 election, according to a poll on Sunday in the Bild am Sonntag newspaper.

The Emnid institute survey found the Christian Democrats and their Christian Social Union allies winning 36 percent of the vote if the election were held on Sunday, unchanged from a similar Emnid poll for Bild am Sonntag taken a week ago.

But the Social Democrats (SPD), led by their chancellor candidate Martin Schulz, continued to slide and lost two percentage points in the week to 29 percent. The CDU/CSU long held a comfortable lead in polls until Schulz was nominated in early 2017 and lifted the SPD to the same levels as the CDU/CSU.

The latest poll, taken just one week before an important state election in Schleswig-Holstein, also showed the CDU/CSU’s preferred coalition partner, the Free Democrats (FDP), rising one point to 6 percent in the last week.

The centre-right alliance would still be well short of winning a majority in parliament with 42 percent.

The far-right Alternative for Germany (AfD) would win 9 percent, unchanged over the week. All parties have said they will not join forces with the AfD, making it more difficult to form the next government.

The SPD’s preferred partner, the Greens, rose 1 point to 7 percent in the last week. The far-left Linke party would win an unchanged 9 percent, according to the latest Emnid poll. The so-called “red-red-green” alliance of SPD, Linke and Greens would also fall short of a majority with 45 percent.

The CDU/CSU and SPD currently lead Germany in a grand coalition government. Both parties have said they do not want to continue that arrangement after the Sept. 24 election.