Social Democratic Party (SPD) leader Andrea Nahles. File photo: REUTERS/Fabrizio Bensch.

Berlin - The surprise announcement of Germany's Social Democrats (SPD) leader Andrea Nahles that she is to resign as head of the centre-left party has prompted questions about the future of Berlin's already shaky coalition government.

Nahles said she would formally declare her resignation as the SPD's first female leader to senior party figures on Monday, after the party sustained heavy losses in last week's EU elections.

"Discussions within the party parliamentary group and feedback from the party have showed me that the support necessary for me to carry out my offices is no longer there," Nahles said on Sunday, following a week of intense pressure after the EU elections delivered the party's worst-ever nationwide result.

The SPD, which is the junior partner in Chancellor Angela Merkel's grand coalition, garnered just 15.8 per cent of votes in the elections to the European Parliament, falling behind the environmentalist Greens for the first time.

The SPD leader said she would also give up her role as head of the party parliamentary group on Tuesday.

It is unclear who will succeed Nahles.

Voters appear to be punishing the SPD for re-entering coalition with Merkel's conservative Christian Democratic Union (CDU) and its Bavarian sister party, the Christian Social Union (CSU), following the 2017 federal elections.

"Together we made a decision to take responsibility for our country as part of the government," Nahles said of the move, which was criticized by voices on the left of party, particularly its youth wing, who wanted to see the SPD go into opposition.

"At the same time, we are working on building the party back up and to convince citizens with new messages," Nahles added.

The CDU party's leadership called on its own party to be prudent in the face of Nahles' announcement, sources told dpa.

Leading party figures said everyone in the CDU should make clear their commitment to the government's mandate, the sources added.

The centre-right party is due to meet later Sunday to discuss the beating they too sustained in the EU poll.

CDU leader Annegret Kramp-Karrenbauer acknowledged that unlike the Greens, who saw a surge in support, her party was unable to attract young people and had not spoken to voters' fears about climate change.