yoni you are sleepy! She's talking about Hk, not Sing. 
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OP, just to put it in context 'nursery' doesn't exist in Hk except for that provided by the government or by various NGOs for low income families who would be unable to sponsor a helper.
That gives you 2 options- expat nanny or helper. A nanny would cost you roughly the same as a nanny in London. You have to sponsor them and be their sole employer. However they do not have to live in. You may be able to find a nanny who is already in HK on a dependency visa or who is a permanent resident and then you would not have to sponsor them. The costs would be the same though in terms of salary. There are various agencies for nannies but they cost around $200/hr so mainly for emergency cover.
Helpers are the more usual option. Costs are as outlined by Yoni. Try to get a recommendation. Legally they must live in unless they are a permanent resident ( these do exist but are few and far between. You are their sponsor and they must work solely for you. They do not have any formal qualifications but many have a fair bit of relevant experience.
Once they get to 2 yrs the options become more flexible as they can go to pre-school unaccompanied, although 2.6 is more usual and some won't take them totally unaccompanied until they're potty trained. Once they're 3, all kids are typically in kindy half days for 5 days a week. However, you still need cover for the rest of the day. Some children do full day at preschool but its rare and usually involves someone pick them up for lunch and them attending 2 different schools in the morning and afternoon.
Anyway, the main issue for the working parent is that there is no concept of wrap around care in any Hk Pre-school.The doubling up of pre-school ed as childcare doesn't happen as it would in the uk.
In practice, Mist working parents use a combination of helper and various classes, playgroups etc for babies and then helper plus pre-school as they get older
Hth