The US State Department has warned citizens of the country to "exercise increased caution" in China amid a heightened detention risk and a ban from exiting the country, Reuters reported.

"U.S. citizens may be detained without access to U.S. consular services or information about their alleged crime," the State Department said in a security alert.

According to the statement, US citizens may face "prolonged interrogations and extended detention" for reasons related to state security.

"Security personnel may detain and/or deport U.S. citizens for sending private electronic messages critical of the Chinese government," it added.