While Hong Kong attracts visitors from all sorts of origin, and hence I cannot be certain who you saw, chances are that you bumped into a large group of Foreign Domestic Helpers.
Summary: Some of them are from Indonesia, a majority Muslim country. They can be seen in many places in Hong Kong on Sundays as it is (usually) their rest day. The hiring of foreign domestic helpers are legal but not without controversy.
Foreign Domestic Helpers in Hong Kong - What's that?
Foreign Domestics Helpers are people who are hired mainly by middle and upper class families to perform domestic duties (in other words, housework).
Their service are required as it is the norm in Hong Kong for both parents to work during daytime.
Where are the women from and what brings them to Hong Kong?
The Association of Hong Kong Agencies for Migrant Workers Limited, who represents some local agents who recruit Foreign Domestic Helpers, gives the following information of the workers' origin (they are overwhelmingly female):
2017 April - Summary
- Filipino - 193 680
- Indonesian - 156 569
- Thai - 2 506
- Others - 6 145
Total = 358 900 (+ 1322)
They are in Hong Kong (hopefully) because they perceive a better economic opportunity there, just like how expats move around the globe. Though the full picture is slightly different - see below for a comment on the current situation.
You also asked:
I am also wondering why so many Muslim women, because earlier impressions e.g. from parks have led me to assume that individual care-takers for elderly locals are typically girls perhaps from (if I had to make a guess based on their appearances) Vietnam or the Philippines.
As shown above, since a significant of them comes from Indonesia, a majority Muslim country, and this demographic group accounts for 2% of the population in Hong Kong (now around 7.5 million), it will be quite easy to bump into them.
Is this a well-know pattern and sight on Sundays in Hong Kong (in the Causeway Bay area)?
Let's start with the when (Sunday).
Foreign Domestic Helper's mobility during workdays (usually Monday-Saturday) are somewhat restricted to the household they are employed in by the Immigration rules in Hong Kong:
Q15:What are the restrictions on deployment of a foreign domestic helper (FDH)?
An FDH is admitted into Hong Kong for full-time, live-in employment with a specific employer to perform domestic duties at the employer's residence specified in the Standard Employment Contract(the Contract) (ID407).
However, by the labour laws in Hong Kong, which I cite the Holidays section on a leaflet for employers, a foreign domestic helper is entitled to have one rest day in every 7-day period on top of the statutory holidays and annual leave entitlement. The absolute majority of the employers choose Sunday as the rest day. On their rest day, they can go wherever they want.
As a result, it is common to see groups of foreign domestic workers congregating in various areas around Hong Kong, including Causeway Bay (or Victoria Park) and Central (on the walkway system near International Finance Centre).
Have I had perhaps had a random glimpse into the underbelly of the Hong Kong economy?
The hiring of foreign domestic helpers are legal, covered by the respective Immigration and Labour laws.
However, they are not well paid in Hong Kong standard. According to the help page on Hong Kong Government website:
You should pay a foreign domestic helper a salary that is no less than the Minimum Allowable Wage (MAW) announced by the Government and prevailing at the date of signing the employment contract for employing the foreign domestic helper. The MAW is currently set at HK$4,520 per month.
Under the Standard Employment Contract, you must provide the helper with suitable accommodation and with reasonable privacy, free food (or food allowance in lieu, which is HK$1,075 per month at present) and free passage from the helper’s home country to Hong Kong and return to the home country on termination or expiry of the contract.
It is also not without controversy. Abuse and mistreatment from some rogue employers/agents (e.g. what covered by this opinion article) gets featured on news occasionally, and from time to time there are demonstrations on worker rights (including pay).