Below it is an article published by The Guardian:

China says it has detained a Taiwanese NGO worker and human rights activist on suspicion of endangering national security, amid worsening relations between Beijing and Taipei and an ongoing crackdown on civil society. Lee Ming-cheh, a volunteer for the Taiwan Association for Human Rights, disappeared on 19 March after crossing into China from the semi-autonomous city of Macau.

His whereabouts were unknown despite repeated inquiries from Taiwan’s government until Tuesday, when the head of China’s Taiwan Affairs Office said Lee was being investigated. He has been prevented from meeting lawyers and his exact location is unclear.

Beijing considers Taiwan to be a part of its territory, and the democratic self-ruled island has oscillated for years between closer ties with China and striking a more independent posture.

Lee, 42, previously worked for Taiwan’s ruling Democratic Progressive party, which was swept into power last year. Since the election of president Tsai Ing-wen, relations between the self-ruled island and Beijing have markedly worsened, with Chinese officials wary of the DPP’s nominally pro-independence stance.

Lee had travelled to China frequently over the past decade without incident, although he had books on political topics confiscated last year. On his most recent trip he planned to see friends and buy Chinese medicine for his mother-in-law.

International human rights organisations rallied to Lee’s defence after China announced it was holding him.

“The secrecy surrounding his case and the government’s record of mistreating activists raise concerns about Lee’s wellbeing,” Maya Wang, China researcher for Human Rights Watch, said. “Human Rights Watch calls on the Chinese government to release him, and to allow him access to family and lawyers.”

His detention is the first of a foreign NGO worker since a controversial law regulating foreign NGOs in China came into effect. Several NGOs were forced to shut down operations in China in the wake of the law’s passing, and campaigners have said it represents President Xi Jinping’s tightening grip on civil society. The law requires any groups from outside mainland China to register with police and to find a local sponsor.

“The unchecked powers the authorities now have to target NGOs and their partners are frightening,” said Nicholas Bequelin, East Asia director at Amnesty International. “Lee Ming-cheh’s detention on vague national security grounds will alarm all those that work with NGOs in China.”

Friends in Taiwan believe Lee was being held due to his efforts to tell mainland Chinese friends about Taiwan’s political culture. He used WeChat, a Chinese messaging service highly susceptible to government monitoring, to discuss China-Taiwan relations, democracy and Taiwan’s president Tsai, according to the Associated Press. His account was later shut down.

China has little tolerance for democratic activism, and discussions on social media can easily lead to a visit from the police. Celebrated human rights lawyer Pu Zhiqiang spent 19 months behind bars for a series of tweets, and was later handed a suspended prison sentence.