A deadly blaze tore through several high-rise apartment towers in Hong Kong on Wednesday, killing at least 13 people and setting off an urgent rescue effort for an unknown number of people trapped inside. The cause of the fire was not immediately known. Hundreds of firefighters struggled to contain the inferno, which apparently started in one building in the Tai Po district around 2:50 p.m. local time. The flames spread across multiple high-rise towers and sent smoke billowing across the city’s northern New Territories. Several buildings were still ablaze late into the evening, more than six hours after the fire started. The towers are in a dense complex known as Wang Fuk Court that includes about 2,000 apartments. Built in the early 1980s, they were sheathed at the time of the blaze in bamboo scaffolding, which is widely used in Hong Kong to construct and repair buildings. A fire services department official said at a news briefing that 13 people had died, including a firefighter, and at least 15 others were injured. A government spokeswoman had said earlier that three of the first five injured people treated at hospitals were in critical condition, according to a report from the city’s hospital authority. The authorities raised their most severe fire alarm for the first time in nearly two decades. Officials with the police and fire services said they had received numerous calls for help from residents trapped inside the buildings. Herman Yiu Kwan-ho, a former district councilor in Tai Po, said that he was in touch with a group of local residents, some of whom live in one of the buildings that caught fire. “More than 10 residents said their family members are still at their homes,” he said by phone. The Hong Kong Fire Services Department said that it had sent 760 rescuers to the site. John Lee, the chief executive of Hong Kong, said that he was activating the city’s Emergency Accident Monitoring and Support Center.