When you try to leave China, you're checked against a no-exit list and simply prevented from leaving if you're on it. No reason need be given to you. China currently keeps a number of political hostages this way and prevents undesirable nationals from leaving the country.
Most countries try to prevent undesirables from entering, china allows them to enter and then prevents them from leaving.
Most countries try to prevent undesirables from entering, china allows them to enter and then prevents them from leaving.
https://fox8.com/2019/01/03/us-warns-citizens-traveling-to-c...