This is a case of force majeure, which the Exit and Entry Administration Law of the People's Republic of China uses in 2 cases. Unfortunately not for this situation:
- punctual exit impossible due to force majeure
but Article 55 (unforeseen arrival in China) states that you must
immediately report to the nearest exit/entry border inspection authority or local public security organ, and accept supervision and administration.
Since all visitors are required to register with the public security bureau (PSB) anyway:
From FAQ China: Foreign Nationals Must Register Their Residence with Local Police within 24 Hours:
Foreign nationals in China must register their temporary residence with the public security bureau (PSB). Further, registration is a prerequisite to filing with the PSB Exit-Entry Division an application for a new visa, stay certificate, or residence permit.
I assume that you are already registered (Hotels do this for you, see Q3 ; otherwise Q4).
Q6: What evidence of registration will be provided to you when you register?
This states that you should have a Registration Form of Temporary Residence
Q7: If your application to the PSB for a new visa, stay certificate, or residence permit is pending, can you use the acceptance receipt to register?
If you’ve applied to the public security bureau’s exit-entry division for a new visa, or residence permit, you should (at least in theory) be able to use the acceptance receipt for your pending application to register your temporary residence.
Since it is now clear that you cannot leave, you should now apply for a new visa or stay certificate for the duration of the force majeure.
(Comment from @MattDouhan: The PSB, where you register, is actually the closest Police Station - so they should be able to help.)
Since it should be clear that you cannot leave, this will probably be noted within the bureaucratic system and may be of help when leaving.
Since by re-registering with the PSB, you are following existing regulations during the force majeure, there is nothing more that you can do. To do nothing at all would be a mistake.
Informing your Embassy or nearest Consulate of your present situation is strongly advised.
This should include photos of
- Passport main page
- pages with visa and entry stamp
- all Registration Form of Temporary Residence that you may have
so that a Consulate official will have all relevant information that may possibly be needed.