The US state department has urged Americans to “exercise increased caution” when travelling to China after a spate of high-profile detentions.
Its updated advice says dual US-Chinese nationals are at particular risk from so-called exit bans that prevent them from leaving.
Canada also revealed that 13 Canadians had been detained since 1 December.
On that day, a top Chinese executive was arrested in Canada at the request of US prosecutors.
Huawei chief financial officer Meng Wanzhou was detained in Vancouver and faces extradition to the US to face fraud charges, which she denies, that are linked to allegations of avoiding US sanctions on Iran.
China has dismissed the US travel warning as unjustified.
“To be frank, the issuance of such a travel advisory by the US side does not hold water,” foreign ministry spokesman Lu Kang said.
“From January to November 2018, 2.3 million visits to China were made by Americans, which means 70 per 10,000 American people made the trip, a ratio far higher than that of the Chinese visiting the US.
“So, this figure is a testament to China’s safety.”