At least 55 people were killed after a massive fire tore through a high-rise housing complex in Hong Kong, authorities said Thursday, the city’s deadliest blaze in decades. Police in the Chinese territory have arrested three people.

Axar.az informs, citing NBC news, though the origin of the fire is unclear, investigators are focusing on the bamboo scaffolding and green netting that surrounded towers undergoing renovation at Wang Fuk Court in the northern district of Tai Po. Experts say they appeared to help flames jump from building to building as the blaze built into an inferno that firefighters were still battling more than 24 hours later.

Police searched the offices of Prestige Construction and Engineering Company, the registered contractor hired to carry out the renovations, after earlier arresting two directors and an engineering consultant on suspicion of manslaughter.

John Lee, Hong Kong’s top leader, said officials were investigating whether protective materials on exterior walls met fire-retardant standards, and that legal action would be brought if necessary.