German Interior Minister Horst Seehofer, who has sparred with Chancellor Angela Merkel over migration at a time of falling support for the governing coalition, will resign as leader of his Christian Social Union, party sources said.

The firebrand conservative also intends to step down as minister before the end of this legislative period, sources from the CSU who held discussions with Seehofer told dpa late Sunday.

Seehofer is expected to give a public statement on his resignation in the coming week, with a new leader to be elected at a conference early next year.

The 69-year-old did not give a timeframe for stepping down prematurely as interior minister, sources said, although he implied that he would not want to stay in the role if he gave up his position as CSU leader. The current legislative period is due to end in 2021.

"2019 will be the year of renewal for the CSU," sources quoted him as saying.

Once a staunch ally of the chancellor, Seehofer's very public spat with Merkel over migration and border security earlier this year has been widely blamed for plunging popularity for all three governing parties: his CSU, Merkel's Christian Democrats (CDU) and the centre-left Social Democrats.

The CSU veteran, who has faced repeated calls to resign as interior minister, also became embroiled in a dispute over the extent of xenophobic violence during protests in the eastern German city of Chemnitz, when he threw his backing behind the country's now-ousted intelligence chief who appeared to downplay the unrest.

CDU support plummeted by over 10 percentage points in elections for the Bavarian parliament last month, causing the party to lose its absolute majority in the only state in which it is on the ballot.

It also performed poorly in the general election in September 2017, losing ground to the far-right Alternative for Germany (AfD).

News of Seehofer's planned resignation comes at a turbulent time in German politics.

After a disastrous state election in Hesse last month, Merkel also announced she would resign as leader of her CDU party and said that this term as chancellor would be her last in politics.

Seehofer's most likely successor as CSU head is Markus Soeder, who already succeeded his party colleague as Bavarian state premier in March.

It is unclear who would succeed Seehofer as interior minister.