US State Department sent a security alert to all US citizens in China to warn them to be extra cautious because of an increased risk of detention and exit bans that prevent foreign citizens from going home.
Washington wrote in an e-mail that they could face prolonged spells in jail without consular support, or access to details of any alleged crime.
The warning comes days after Beijing passed a national security law fro Hong Kong, with the law, drafted to apply for people from outside Hong Kong, including foreign nationals.
Human rights activists and lawyers pointed out that China could potentially use the legislation to bring sue any person from any country - to censor freedom of expression and mute critics around the world.
The State Department did not elaborate more details, but it emphasized that criticism of the Chinese government, even in private communication, could lead to detention and legal proceedings.
Local authorities may detain or deport US citizens for sending private electronic messages critical of the government and the Communist Party, the letter noted.
The security alert comes at a time of escalating tensions between Washington and Beijing. On Friday, President Trump commented that the international relations between the United States and China had been "severely damaged."
The US government has heavily criticized the controversial security law that Beijing imposed on Hong Kong in June. President Trump has also been vocally critical over the Chinese handling of the coronavirus spread. According to Trump, Beijing failed to provide accurate information to the public about the pandemic in its early stages.
Furthermore, Washington announced visa bans and an asset freeze on three Chinese officials citing human rights abuses in Tibet and Xinjiang provinces.
Earlier last week, Canada and Australia also issued travel warnings over fears of arbitrary detentions in Hong Kong. In response, Beijing labeled Australia's concerns as "completely ridiculous and disinformation."
Canada accused Beijing of hostage diplomacy over the arrest of two Canadians, Michael Kovrig and Michael Spavor, who were charged with espionage after more than a year in prison.
Michael Kovrig is a former diplomat, while Michael Spavor is a businessman. They were detained in 2018, soon after Canada arrested Meng Wanzhou, the chief financial officer of Huawei, on a US extradition warrant.
Justin Trudeau said he was extremely disappointed that Beijing linked the two Canadians to the judicial proceedings against Meng. He pressed China to release them on numerous occasions.
China has always declined the accusations that any of its criminal proceedings against foreign citizens are political.
What do you think? Do you think that international blackslash would make China revoke the controversial law?