Authorities on Friday afternoon put the death toll at 128 but warned that more charred remains could be found as investigators combed the towers.
With at least 150 people still missing from Wednesday's tragedy, the death toll is expected to rise.
On Saturday morning, top officials, among them Chief Executive John Lee, stood in silence for three minutes outside the government headquarters.
Until Monday, flags at all government buildings will be flown at half-mast.
Meanwhile, in response to the blaze, China is launching a fire safety inspection campaign for high-rise buildings across the country.
The focus of the campaign will be buildings undergoing external wall renovations and interior modifications, the Ministry of Emergency Management said in a statement on Saturday.
There will be four key areas of inspection, namely scrutiny of flammable materials used in external wall insulation systems, prohibited construction materials such as bamboo scaffolding, fire safety equipment, and evacuation routes.
Hong Kong's fire department was alerted to the fire at the residential complex shortly before 3 p.m. (0700 GMT) on Wednesday.
The fire department said it received reports on Wednesday at 2:51 p.m. (0651 GMT) of a fire in the residential complex. It was upgraded to a Number 4 alarm at 3:34 p.m. and as night fell it was declared a five-alarm fire, the highest level.
It would go on to burn for more than 40 hours and engulfed seven of the complex's eight buildings before being finally extinguished on Friday morning.
It is Hong Kong's deadliest blaze since 1948, when 176 people died in a warehouse blaze, and has prompted comparisons to London's Grenfell Tower inferno, which killed 72 people in 2017.