Contractors working on the renovations used these substandard materials in hard-to-reach areas, effectively hiding them from inspectors, Chief Secretary Eric Chan said.
Foam insulation used by contractors also fanned the flames and fire alarms at the complex were not working properly, officials have said.
Thousands of residents have turned out to pay tribute to the victims, who include at least nine domestic helpers from Indonesia and one from the Philippines.
Vigils are also due to take place this week in Tokyo, Taipei and London.
SEARCH MOVES TO WORST AFFECTED BUILDINGS
The remaining buildings being scoured for remains are the worst damaged and the search may take weeks, authorities have said.
Images shared by police showed officers clad in hazmat suits, face masks and helmets, inspecting rooms with blackened walls and furniture reduced to ashes, and wading through water used to douse fires that raged for days.
More than 60 pets, including 34 cats, 12 dogs and 7 turtles, perished in the fire, the Society for the Prevention of Cruelty to Animals said. More than 200 were rescued.
The apartment blocks were home to more than 4,000 people, according to census data, and those who escaped must now try to get their lives back on track.
Nearly 1,500 people have been moved out of evacuation centres into temporary housing, with a further 945 put up in youth hostels and hotels, authorities said.
With many residents leaving behind belongings as they fled, authorities have offered emergency funds of HK$10,000 (US$1,284) to each household and provided special assistance for issuing new identity cards, passports and marriage certificates.
Source: CNA
