A fire that spread from a fourth-floor mental health clinic in an eight-storey building in western Japan has left 24 dead in what police are treating as a possible arson.

Police are searching for a man in his 50s or 60s who witnesses saw carrying a paper bag which was dripping an unidentified liquid. He may have been among the 24 dead, or is one of the three people who were resuscitated and remain in serious conditions, or may have fled, a police investigator said.

Fire crews who reached the building in the business, shopping and entertainment area of Kitashinchi in central Osaka found 27 people in a state of cardiac arrest, said fire department official Akira Kishimoto.

One woman was conscious and brought down by an aerial ladder from a window on the sixth floor and was being treated in hospital, he said.

Later on Friday, 24 people were pronounced dead, the fire department said. It added that three others were resuscitated and are in serious conditions.

In Japan, authorities customarily describe those without vital signs as being in “shinpai teishi” or a state of cardiac and pulmonary arrest, and do not confirm deaths until they are pronounced in hospital and other necessary procedures are done.

A doctor at one of the hospitals treating the victims said he believed many of them died after inhaling carbon monoxide as they had limited external injuries.

The building houses the mental and internal medicine clinic, an English language school and other businesses.

Most of the victims are believed to have been visitors at the clinic on the fourth floor, fire officials said.

The cause of the fire and other details were not immediately known. Osaka police earlier said they were working to determine whether the fire was caused by arson.

They later set up a team at the prefectural police headquarters, a sign they strongly suspect arson and murder.

According to NHK, a female outpatient at the clinic’s reception desk saw the man being sought by police. Another person nearby said the fire started soon after he put the leaky bag next to a stove on the floor and kicked it, with more liquid pouring out.

A clinic psychiatrist, Kotaro Nishizawa, could not be reached after the fire, NHK said. It quoted his father as saying the doctor hinted at a problem at the clinic but did not elaborate.

People on other floors of the building are believed to have been safely evacuated, fire officials said.

NHK quoted a witness as saying she heard a woman’s voice coming from the fourth floor calling for help. Another witness told TV Asahi he saw flames and smoke coming out of windows on the fourth floor when he stepped outside after hearing a commotion.

In total, 70 fire engines were mobilised to fight the fire, which was fully extinguished more than six hours later, officials said.

In 2019 at the Kyoto Animation studio, an attacker stormed into the building and set it on fire, killing 36 people and injuring more than 30 others.

In 2001, an intentionally set blaze in Tokyo’s Kabukicho entertainment district killed 44 people — the country’s worst known case of arson in modern times.