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 warns that US citizens have been arbitrarily prevented from leaving the country.
The warning comes as two Canadian citizens remain in detention in China.
Former diplomat Michael Kovrig and businessman Michael Spavor were arrested last month as relations between the two countries worsened.
The pair face accusations of harming national security and, on Thursday, China’s top prosecutor said they had “without a doubt” violated the law.
Separately, three US citizens were accused of committing “economic crimes”and barred from leaving China in November.
Victor and Cynthia Liu, who are the children of a fugitive businessman, and their mother, Sandra Han, have reportedly been detained since June.
“US citizens may be detained without access to… consular services or information about their alleged crime,” the advisory reads.
“Individuals not involved in legal proceedings or suspected of wrongdoing have also been subjected to lengthy exit bans in order to compel their family members or colleagues to co-operate with Chinese courts,” the state department said in a separate warning issued last January.
The latest advice also warns of “special restrictions” on those who hold dual US-Chinese citizenship.
Dual-citizenship is not allowed under Chinese law, and the state department has warned that US-Chinese nationals can be detained and denied US assistance in China.
It advises travelling on a US passport with a valid Chinese visa and asking officials to notify the US embassy immediately if you are detained or arrested.