Twenty people sent to China by a South African charity, many of them British, have been detained, with some of them accused of watching "propaganda videos".
Gift of the Givers, a disaster relief charity based in South Africa's Pietermaritzburg, said 20 of its associates were held on Friday at Ordos airport in China's Inner Mongolia region.
It said 10 were South Africans, nine British, and one an Indian national.
"No reasons were given for the arrest. The Chinese, now trying to find reasons for the detention suggested that some members were linked to a terror group," it added.
The group's founder, Imtiaz Sooliman, said on Wednesday that 11 of the detained - five South Africans and six Britons - had been released and would return home.
The nine others "are being held without charge at a detention centre on the accusation that they were watching propaganda videos", the group said on a Facebook page.
The families of the five South Africans still detained were "looking for an international human rights lawyer, but to help them with what?" Sooliman said. "They have no idea why they're being held."
The public security ministry in Beijing did not immediately respond to a request for comment by AFP.
Gift of the Givers describes itself on its website as being inspired by Muhammed Saffer Effendi al Jerrahi, a master of Sufism, a mystical form of Islam.
The group, which has provided medical equipment and training in multiple countries in Asia and Africa, says its staff are "facilitators of Almighty God's Aid... distributing it from Him to all of mankind".
Chinese regulations passed in 2000 ban foreigners from all missionary activity including "distributing religious propaganda materials".
The ruling Communist party, suspicious of overseas groups, has in recent months tightened controls on foreign charities working in the country.
The South Africans were originally detained "with no access to communication or legal representation" and included several doctors, Gift of the Givers said.
The group's planned 47-day tour of China had gone "horribly wrong", it added.
A spokeswoman for the British embassy in Beijing said on Wednesday that 11 British citizens had been held in northern China, two of whom held South African dual nationality.
Six would be deported "shortly", spokeswoman Natasha Simpson said, adding officials were seeking "further clarifications" on the detentions.
South African foreign affairs ministry spokesman Nelson Kgwete told local television that the government had been informed "about the arrest of 10 South African citizens in China" and the embassy was providing consular assistance.