German Health Minister Jens Spahn has renewed his criticism of Chancellor Angela Merkel's refugee policies as he intensifies his campaign to replace her as the head of the Christian Democratic Union (CDU) in December.

Writing in Thursday's edition of the national daily Frankfurter Allgemeine Zeitung, Spahn said that policies on refugees and migration are the most important reasons the CDU has lost the confidence of its supporters.

He described Merkel's refugee policy as "the elephant in the room."

Spahn, 38, is one of three CDU politicians so far seeking to take over as party leader at its December conference after Merkel said this week she would not run but would continue as chancellor until her term ends in 2021.

He called for the CDU and its Bavarian sister-party, the Christian Social Union (CSU), to get over their conflict regarding Merkel's 2015 decision to open the borders to hundreds of thousands of refugees.

But Spahn said that despite denials, the migration issue was still current. Germany continued to experience "annual disorderly, overwhelmingly male immigration" that he put at a level of around 200,000.

He noted that promises to protect the external borders of the European Union had not been kept and that redistribution and integration of migrants had not been achieved.

Spahn denied that he planned to take the CDU to the right, saying his aim was to introduce policies of common sense, civilized values and integrity.