HONG KONG — A catastrophic fire that engulfed seven residential towers in Hong Kong’s Tai Po district has killed at least 51 people and left hundreds missing, marking the city's deadliest residential blaze in over 60 years. 

With many questions still unanswered, here’s a breakdown of what is known about the incident.

How did the fire start and spread so quickly?

The exact cause is still unclear, but authorities have confirmed the fire started on the bamboo scaffolding of one of the buildings, Wang Cheong House, which was undergoing renovation.

The fire's rapid and intense spread is being blamed on a combination of factors. 

Hong Kong’s Secretary for Security, Chris Tang, said the "protective netting, waterproof cloth and plastic sheeting" on the scaffolding burned "far more intensely" than compliant materials should, according to a Bloomberg report.

Fire officials also noted that Styrofoam found at the scene accelerated the blaze. Compounding the issue, residents reported that fire alarms failed to go off, with many only alerted when a security guard knocked on their doors.

What about the building complex?

The Wang Fuk Court complex, built in the 1980s as government-subsidised housing, is a densely populated estate estimated to house nearly 5,000 people. 

Like many Hong Kong estates, it is common for multi-generational families to live in a single small apartment. The seven affected towers were undergoing a lengthy renovation and were covered in bamboo scaffolding and mesh.