A Chinese official said on Thursday that a group of foreigners had been detained for distributing "terrorist" materials after a South African charity said nine were being held.

Gift of the Givers, a humanitarian relief organisation based in South Africa, said five of the detainees were South Africans, three British and one Indian.

They were among a total of 20 visitors held on Friday at Ordos airport in China's Inner Mongolia region, it said, adding none had been charged.

"Foreign tourists have been detained by the police here, I heard they looked at and propagated something about violence and terrorism," Zhang Xi, an official at Ordos's foreign affairs office, told AFP Thursday.

Local police declined to comment on the case.

The nine still held are at a detention centre, Gift of the Givers said in a statement.

"The Chinese have been very vague saying that someone in the group has some links to a suspected terror group and that someone has some links to a banned group and that the real reason for the incarceration is that someone was watching propaganda videos in the hotel," it said.

The British embassy in Beijing said five of those still being held were British citizens. Two of the original detainees were British-South African dual nationals, it said earlier.

The South Africans held at the airport included several doctors and relatives of prominent businessmen, Gift of the Givers said, adding that the travellers' planned 47-day tour of "ancient China" had gone "horribly wrong".

African telecommunications giant Vodacom confirmed that the brother, aunt and uncle of the company's chief executive Shameel Joosub were among them.

Gift of the Givers founder Imtiaz Sooliman told AFP that Joosub had asked it to assist as it has experience with international emergencies.

Several of the group held at the airport on Friday have been released and have left China.

South African deputy president Cyril Ramaphosa is on an official visit to China and Foreign Minister Maite Nkoana-Mashabane told reporters in Pretoria that consultations with Chinese authorities were ongoing.

"The matter has been raised at the highest level possible, taking advantage of the deputy president's presence in China," she said.