Found it!

http://www.china.org.cn/government/central_government/2008-10/16/content_16619015.htm

Article 25 of “The Law of the People's Republic of China on Control of the Entry and Exit of Alien”, which was passed in December 1986 (hence, your interesting 26 years) - “Aliens who reside or stay in China and are 16 years of age or older must carry their residence permits or passports on them for examination by the police of foreign affairs when the occasion requires.”

As for the reference, “residence permits or passports”, up to 2005, ‘Foreigner Residence Permits’ were not placed in passports; they were a greenish-blue booklet.

I also discovered that, in 1985, China’s lawmakers passed the ‘Identity Card Bill’ which required all citizens over the age of 16 apply for identification cards. And in June 2003, China’s lawmakers amended the ‘Resident Identity Bill’ to the effect that Chinese citizens aged 16 and above must carry identification in public at all times.

Whilst the ‘Resident Identity Bill’ does not refer to foreigners, it would seem that foreigners' burden of carrying I.D. at all times is no more onerous than applies to Chinese nationals.