A massive fire ripped through a psychiatry clinic in Osaka, Japan, on Friday after a patient carried a bag into the building that was leaking flammable liquid.

Reuters, citing the Yomiuri newspaper, described the patient as an elderly man. Other reports said police in the city were investigating possible arson. Twenty-seven people are feared dead.

Fire engines park near a building, center in the background, where a fire broke out in Osaka, western Japan Friday, Dec. 17, 2021. (Yukie Nishizawa/Kyodo News via AP)

Fire engines park near a building, center in the background, where a fire broke out in Osaka, western Japan Friday, Dec. 17, 2021. (Yukie Nishizawa/Kyodo News via AP) (Yukie Nishizawa/Kyodo News via AP)

All of them have since been taken to nearby hospitals. 

Rescuers attend to victims following a fire at a building in Osaka, western Japan Friday, Dec. 17, 2021. (Kyodo News via AP)

Rescuers attend to victims following a fire at a building in Osaka, western Japan Friday, Dec. 17, 2021. (Kyodo News via AP)

Four people have been pronounced dead, NHK national television and other media reported, but Japanese authorities declined to confirm. 

Firefighters work at the scene where 27 people were feared dead after a blaze at a building in Osaka on December 17, 2021. (Photo by Philip FONG / AFP) (Photo by PHILIP FONG/AFP via Getty Images)

Firefighters work at the scene where 27 people were feared dead after a blaze at a building in Osaka on December 17, 2021. (Photo by Philip FONG / AFP) (Photo by PHILIP FONG/AFP via Getty Images) (PHILIP FONG/AFP via Getty Image)

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

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"We don’t know the details yet, but small multi-tenant buildings sometimes have only one emergency staircase," Ai Sekizawa, an expert on fires at Tokyo University of Science, told NHK, according to the New York Times. He called the fire "shocking."

The Associated Press contributed to this report