A huge fire still burning in a Hong Kong apartment complex that has killed at least 55 people and left nearly 300 missing may have been caused by a "grossly negligent" construction firm using unsafe materials, police said on Thursday.

Almost a full day after the fire began, firefighters were struggling to reach residents potentially trapped on the upper floors of the Wang Fuk Court housing complex due to intense heat and thick smoke from the blaze that erupted on Wednesday afternoon.

The tightly packed complex in the northern Tai Po district has 2,000 apartments in eight blocks that are home to more than 4,600 people in a city struggling with chronic shortages of affordable housing.

"We bought in this building more than 20 years ago. All of our belongings were in this building, and now

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