At least 24 are dead after a medical clinic in the Japanese city of Osaka caught fire on Friday in “one of the deadliest blazes in Japan in about two decades,” The Washington Post reports.

Osaka police are currently investigating the incident and working to determine whether it was an accident or arson, per CNN. The blaze reportedly began in a psychiatric care clinic on the building’s fourth floor, where a patient in his 50s or 60s “was seen holding a paper bag with liquid leaking from it,” the Post reports, per Mainichi Shimbun, a Japanese news outlet. The man, now the potential arson suspect, was in the hospital in critical condition as of Friday evening in Japan.

The fire broke out around 10:30 a.m. local time and was brought under control within 30 minutes, according to the Post. Rescue teams brought 27 people to the hospital, and three were temporarily revived, though it is unclear whether they survived. 24 others died.

Victims were believed to be attending a meeting of a weekly mental health program when the fire broke out. Their ages range from the 20s to the 60s. Read more at The Washington Post.