HONG KONG (AFP)

Authorities said Monday they had made a total of 13 arrests over Hong Kong's deadliest fire in decades after the blaze killed 151 people last week, a toll that could rise further.

The arrests were made on suspicion of manslaughter as investigators work to piece together what led to the catastrophic fire taking hold so fast in a complex of high-rise apartments.

Officials have been looking at factors including the styrofoam panels and bamboo scaffolding use in a renovation project at the site.

Officials also announced Monday that some of the exterior netting used on scaffolding at the housing estate did not meet fire-resistance standards.

Police representative Tsang Shuk-yin on Monday told a news conference that as of 4 pm (0800 GMT) the fire killed 151 people, up from Sunday’s toll of 146.

“We cannot rule out the possibility of this number increasing further,” Tsang said.

The blaze that engulfed Wang Fuk Court in Hong Kong's northern Tai Po district was the world's deadliest residential building fire since 1980.

Police have completed searches in five of the estate's eight high-rise blocks.

Tsang said that "some remains have already been reduced to ashes" and that it was possible that some of the people reported missing will not be recovered.

Police found the remains have been found inside apartment units, in hallways, and on staircases, and will continue to search the buildings, he said.

Thirteen people have been arrested for manslaughter in relation to the blaze, Chan Tung, director of crime and security of the Hong Kong Police Force, told another news conference.

The group included 12 men and one women aged between 40 and 77.

Officials also announced that some of the exterior netting used on scaffolding at the housing estate did not meet fire-resistance standards.

Seven of the 20 samples collected at various locations in four buildings of Wang Fuk Court did not meet fire-resistance test standards, said chief secretary Eric Chan.

The city has seen an outpouring of grief in recent days.

Thousands have laid flowers and paid their respects over a three-day mourning period, with some of the notes left at the site calling for accountability.