Jerome a Paris:

banks' clearing accounts (Aggregate Balance) maintained with the HKMA for the purpose of clearing and settling transactions between the banks themselves, and also between the banks and the HKMA

plus the fact that the HKMA maintains foreign reserves in an amount sufficient to back all the monetary mass of Hong Kong means that it fulfills all the functions of a central bank even if it isn't called a central bank.

Can we please step away from the nominalist debate for a bit and just look at the functions of the institutions?

By laying out pros and cons we risk inducing people to join the debate, and losing control of a process that only we fully understand. - Alan Greenspan