In total, six people from Oi Fai House at Yau Oi Estate have come down with the virus.
On Friday night, authorities partially evacuated the building after experts warned that the virus was likely transmitted via the building’s pipes.
Residents living in units 09 on every floor of the block were sent to quarantine.
But authorities said on Saturday that two more people from a family living in unit 32 have tested preliminary positive.
The Centre for Health Protection said investigation shows that units 09 and 10, as well as units 31 and 32, separately share a soil pipe.
It said after taking into account expert opinion, it would also send everyone living in units 10, 31 and 32 to quarantine.
The announcement came as officials reported five new confirmed coronavirus cases on Saturday – three imported and two locally acquired.
The two new local cases include a 66-year old man and a 6-year-old boy from Oi Fai House.