Updated 11.54am with China reaction.
Berlin on Tuesday called allegations that an aide of a far-right German MEP was spying for China "very serious" and urged a thorough investigation.
"If it is confirmed that spying for China is happening from the European Parliament, then that is an attack on European democracy from within," said German Interior Minister Nancy Faeser.
The man, who is under arrest, was named only as Jian G. He stands accused of sharing information about negotiations at the European Parliament with the Chinese intelligence service and of spying on Chinese opposition figures in Germany, federal prosecutors said in a statement.
On the website of the European Parliament, Jian Guo is listed as an accredited assistant to MEP Maximilian Krah, the far-right AfD party's lead candidate in the forthcoming EU-wide elections.
He is a German national who has reportedly worked as an aide to Krah in Brussels since 2019.
The suspect "is an employee of a Chinese secret service", prosecutors said.
"In January 2024, the accused repeatedly passed on information about negotiations and decisions in the European Parliament to his intelligence service client.
"He also spied on Chinese opposition members in Germany for the intelligence service."
The suspect was arrested in the eastern German city of Dresden on Monday and his homes were searched, they added.
The accused lives in both Dresden and Brussels, according to broadcasters ARD, RBB and SWR, who broke the news about the arrest.
The AfD said the allegations were "very disturbing".
"As we have no further information on the case, we must wait for further investigations by federal prosecutors," party spokesman Michael Pfalzgraf said in a statement.
The case is likely to fuel concern in the West about aggressive Chinese espionage.
Another three arrests on Monday
It comes after Germany on Monday arrested three German nationals suspected of spying for China by providing access to secret maritime technology.
China's embassy in Berlin "firmly" rejected the allegations, according to Chinese state-run news agency Xinhua.
According to German media, the two cases are not connected.
In Britain on Monday, two men were charged with handing over "articles, notes, documents or information" to China between 2021 and last year.
Police named the men as Christopher Berry, 32, and Christoper Cash, 29, who previously worked at the UK parliament as a researcher.
China: Allegations are malicious
Beijing said Tuesday that the arrests and charges in Germany and Britain of people accused of spying for China were designed to "smear and suppress" the country.
China's foreign ministry spokesman Wang Wenbin was asked several questions by journalists on Tuesday about the allegations.
"Recent reports on China's so-called espionage activities in Europe are all hyped up and aimed at smearing and suppressing China," Wang said.
"Not only there have been reports from Germany but we have also noted similar reports from the UK in the past two days.
"We firmly oppose such hype and urge relevant parties to stop spreading false information about the so-called China spy threat, stop political manipulation and malicious defamation against China," he said.
European Parliament suspends aide
The EU parliament on Tuesday announced it had suspended "with immediate effect" the German far-right MEP's assistant who was arrested for allegedly spying for China.
Following the arrest in Germany on Monday of the suspect, Jian Guo, "and given the seriousness of the revelations, Parliament has suspended the person in question with immediate effect," a spokesperson for the legislature told AFP.