A deadly inferno has torn through a massive housing complex in Hong Kong, killing at least 44 people with more than 270 others still missing, in what is likely the most deadly blaze in Hong Kong since World War II.

Firefighters are still trying to get parts of the fire under control more than 20 hours after it broke out.

Questions are mounting about how the fire in a skyscraper-filled city with a usually strong public safety record and construction standards could become so deadly, leaping from building to building.

Here’s the latest:

What is happening: A fire spread across seven towers at Wang Fuk Court, a public housing estate in the Tai Po District that was home to more than 4,000 people. Firefighters are still working to extinguish at least three towers at the complex, which was home to a disproportionately high percentage of elderly residents. There is now a huge concern that the buildings may collapse.

The complex was under renovation and encased in bamboo scaffolding and safety netting – a construction technique ubiquitous in Hong Kong.

Critical injuries: At least 66 people have been admitted to hospital as of 8 a.m. local time, with 17 in critical condition and 24 in serious condition.

Residents displaced: Hundreds of residents are now likely homeless in a city with an acute shortage of housing. Some residents would have waited years for a home in the public estate. About 900 people are in temporary shelters.

Many trapped: Last night, firefighters trying to reach people trapped on upper floors of the burning buildings faced extremely high temperatures and falling debris, hindering rescues, according to the fire department. Last night, fire officials urged those trapped to seal doors and windows with tape and wet napkins.

How China is responding: Chinese leader Xi Jinping expressed his condolences to the fire victims, and designated 2 million yuan ($282,470) to Red Cross emergency assistance. Chinese tech giants Xiaomi and Tencent, as well as apparel conglomerate Anta, announced donations totaling $6.4 million to Hong Kong. Posts about the fire had more than one billion views in mainland China, where social media is strictly monitored by the government.

The investigation: The fire spread in an “unusual” manner, and a criminal investigation has been launched, Security Secretary Chris Tang said. Hong Kong Police said they arrested three men on suspicion of manslaughter — two directors and a consultant of a construction company — and accused them of “gross negligence.” Authorities will also investigate whether building materials complied with fire safety standards.

Historic disaster: The blaze was declared a level five fire, the highest rating used in one of the world’s most densely populated cities, with the highest concentrations of skyscrapers. But Hong Kong has retained a strong track record on building safety, thanks to its high-quality construction and strict enforcement of building regulations.

CNN’s Chris Lau, Jessie Yeung, Kevin Wang and Karina Tsui contributed reporting.