The Foreign Ministry in Beijing summoned the German ambassador Patricia Flor on Thursday to discuss an espionage affair.
German security services have arrested four suspects on allegations of spying for China, including an aide to a prominent politician in the far-right Alternative for Germany (AfD) party, Maximilian Krah.
The German Foreign Office said in a statement that the Chinese chargé d'affaires had already been summoned to a meeting on the matter in Berlin on Tuesday.
"The Federal Government's clear position on the ongoing investigations into alleged Chinese espionage activities was made clear to him," the statement continued.
After her meeting at the Foreign Ministry in Beijing, German ambassador Flor wrote on X, formerly known as Twitter: "A quite telling move – but, after all, a good opportunity to explain a few things: 1) We do not tolerate espionage in Germany, regardless of which country it comes from.
"2) We protect our democracy and our constitutional state by constitutional means. 3) The Federal Public Prosecutor General conducts the investigations. In the end, an independent court will decide on the accusations."
Krah, the AfD's top candidate for June's EU Parliament elections, announced on Wednesday that he will continue leading the party's campaign despite the arrest of his aide.
The aide to Krah was detained in Dresden on Monday on suspicion of passing information from the European Parliament to China, according to prosecutors.
Prosecutors said the suspect had also spied on Chinese opposition members in Germany.
The Chinese government has rejected the allegations, calling them slanderous.