According to Quick Guide for the Employment of Domestic Helpers from Abroad (ID 989), employers who wish to employ a domestic helper from abroad (Helper) have to satisfy the following criteria:

a.	The employer is financially capable of employing a Helper. In general, for every Helper to be employed, the employer must have a household income of no less than HK$15,000 per month or asset of comparable amount to support the employment of a Helper for the whole contractual period;
b.	The Helper and the employer shall enter into a standard Employment Contract (ID 407);
c.	The Helper shall only perform domestic duties for the employer as specified in the standard Employment Contract (ID 407);
d.	The Helper shall not take up any employment with any other person during his/her stay in Hong Kong;
e.	The employer will pay the Helper a salary that is no less than the minimum allowable wage as announced by the HKSAR Government. If no food is provided to the Helper, the agreed amount of food allowance should not be less than HKD$1,121 per month;
f.	The Helper shall work and reside in the contractual address only ;
g.	The employer shall provide the Helper with suitable accommodation and with reasonable privacy;
h.	The bona fides of the employer and the Helper are not in doubt;
i.	There is no known record to the detriment of the employer and the Helper; and
j.	The employer is a bona fide Hong Kong resident.

Useful link: http://www.immd.gov.hk/ehtml/ID(E)989.htm