At least 24 people were killed after a blaze gutted a mental health clinic in a commercial building in the Japanese city of Osaka on Friday, local media said, with police reportedly considering the incident a possible arson. The charred interior of the clinic was visible through blackened and broken window frames as firefighters put up tarpaulin sheets to block the scene from view following the fire that broke out mid-morning and raged for half an hour on the narrow block’s fourth floor. “The municipal fire department is investigating the cause of the fire. I have received a report that Osaka police is investigating the fire as possible arson,” regional governor Hirofumi Yoshimura said on Twitter. Japanese media said a man in his 50s or 60s had allegedly dispersed a liquid to start the blaze. A young woman who witnessed the fire told public broadcaster NHK she had seen a woman trapped on the fourth floor. “She leaned out (from a window) and was saying things like ‘Please help’… She seemed very weak. Maybe she inhaled lots of smoke,” the woman said. Osaka, a major economic hub, is Japan’s second-biggest metropolis after the greater Tokyo region. Deadly fires are unusual in Japan, which has strict building standards, and violent crime is also rare. Dark smoke Prime Minister Fumio Kishida offered his “sincere condolences” to the victims and sympathy to those injured in the incident. “We must get to the bottom of this horrible case. We must clarify the cause and how it happened. And we must take measures to prevent the same thing from happening again,” he said. Dozens of fire engines rushed to the scene of the blaze, which occurred in a busy business area near Kitashinchi train station in the city in western Japan. Most of the eight-story structure’s exterior remained intact after the fire, with around 20 square metres (215 square feet) reportedly burned in the blaze. “There was lots of dark smoke… there was a very strong smell, too,” a middle-aged woman told NHK at the scene. Fuji TV reported that most of those who died in the fire were believed to have suffered from carbon monoxide poisoning. Earlier on Friday, an Osaka fire department official feared 27 of the 28 people injured in the blaze had died. In Japan, only a doctor can officially certify someone dead. One year ago, a man was charged with murder over a 2019 arson attack on a Kyoto animation studio that killed 36 people, the country’s deadliest violent crime in decades. The attack sent shockwaves through the anime industry and its fans in Japan and around the world. A 2008 arson attack on a video shop in Osaka killed 16 people. The attacker is now on death row.