Your passport must be valid for at least 6 months when you enter China.
UK Emergency Travel Documents (ETDs) are accepted for entry, airside transit and exit from China. You may be required to show a police report indicating how you lost your full passport.
If your ETD has been issued in China, you will need an exit visa from the Public Security Bureau before you can leave. This process can take up to 7 working days.
(Information provided by gov.uk)