The US State Department has raised its Travel Advisory for China to Level 2: Exercise Increased Caution.

Reasons include "arbitrary enforcement of local laws" and "special restrictions on dual US-Chinese nationals".

China does not recognize dual nationality, and US citizens of Chinese heritage may be subject to extra scrutiny and harassment, and be denied access to US consular services.

"Exit bans" on dual US-Chinese nationals are a particular concern. Exit bans can be imposed without warning when people try to leave China, and may continue for years.

Actions of the Chinese government probably represent an effort to use tourism as a weapon in its trade war with the US, which the US so far has been largely winning because of the vastly greater quantity of goods it buys from China.

So stand by for some form of retaliation by the Chinese government.

And remember that China accounted for 8% of US overseas arrivals in 2016 - ranking behind only the UK and Japan - and that within a couple of years China will be the largest global tourism source market.