Do Chinese citizens require a visa to go to Hong Kong for less than 7 days?

This is official email reply from immigration officer. The purpose must be in transit. (Malaysia > Hong Kong > Malaysia is not considered as transit)

However, you can make two transits as you suggested (Malaysia > Hong Kong > Shenzhen (you should stay at Shenzhen for at least one day), Then Shenzhen > Hong Kong > Malaysia. They consider this as two independent transits)

Dear Sir/Madam,

Thank you for your e-mail message.
Under the present transit arrangement, holders of People's Republic of China (PRC) passport who are in transit through the Hong Kong Special Administrative Region (HKSAR) to and from another country or territory (e.g. Foreign country > HKSAR > Mainland China or Mainland China > HKSAR > Foreign country) may be granted a stay of seven days on each landing without prior need to obtain an entry permit. However, if a person wishes to come to the HKSAR for purpose other than transit (e.g. Switzerland > HKSAR > Switzerland or Mainland > HKSAR > Mainland), then this is not treated as a proper purpose of transit.

My second Email:

Dear Ms LAI Hin-yan,
Thanks very much for your explanation.
How about I transit at hong kong like this way:
Switzerland>Hong Kong>Shenzhen (6 days transit in Hong Kong)
Shenzhen>Hong Kong>Switzerland (1 day transit in Hong Kong)
I will stay in Mainland Shenzhen city for 7 days and then back to Hong Kong for transit to Switzerland.
Is it possible?

Reply:

Dear Sir/Madam,

Thank you for your e-mail message.

Under the present transit arrangement, holders of People's Republic of China (PRC) passport who are in transit through the Hong Kong Special Administrative Region (HKSAR) to and from another country or territory (e.g. Switzerland > HKSAR > Mainland China or Mainland China > HKSAR > Switzerland) may be granted a stay of seven days on each landing without prior need to obtain an entry permit.

However, they must satisfy the immigration officer on arrival that they meet with the normal immigration requirements and qualify for entry as bona fide visitors, including possession of adequate funds to cover the duration of stay without working and, unless in transit to Mainland of China, the holding of onward tickets.

I hope you will find the information useful.

According to TIMATIC (the Visa system the airline will likely use when you check-in) :

Visa required, except for Holders of a PRC Travel Document (Lu Xing Zheng) containing an entry permit for Hong Kong (SAR China).

Visa required, except for A max. stay of 7 days for: - holders of passports issued by China (People's Rep.), provided passenger is in transit (incl. overland) to/from a third country.

The specific mention of "to/from a third country" means that a return ticket to Malaysia (presuming that is where you flew from) is NOT sufficient, as is it not a third country.

Flying back via Mainland China or Macao is an interesting case, as it is not technically a third country. The text you quoted includes the fact it can be a different region or territory, however Timatic simply says country.

However even if you are allowed do this whilst in transit to Mainland China or Macao, it's fairly clear that what you are suggesting is NOT in the spirit of the exception. To both the airline and the immigration staff it's going to be very clear that you are not in Hong Kong for the purposes of transit whilst on the way to/from another country, which is the intent of this rule, but instead that Hong Kong is your actual destination.

If you were looking to spend 3 days in Hong Kong and then another 3+ in Mainland China or (say) South Korea then you would be fine - but if your sole destination is Hong Kong then I suspect that you will likely face issues either when attempting to board the flight, or at HK immigration.