Police confirmed 24 people died after a fire tore through the upper floors of a small commercial building in Osaka on Friday morning, with officials suspecting arson as the cause of the blaze.

The fire in the city’s bustling Kita Ward was reported at around 10:20 a.m. to the local fire department and appeared to have begun in a medical clinic on the fourth floor of the multistory building, which also contained an English cafe and a small clothing shop, among other tenants.

Windows on the fourth floor were shattered and burn marks were clearly visible to the throngs of office workers, reporters and camera crews gathered at the scene of the blaze, which was just minutes from Osaka Station, one of the city’s main transportation hubs. News helicopters circulated overhead into the afternoon as investigators and fire crews gathered evidence to determine a cause.