Twenty-seven people were feared dead after a blaze at a building in a commercial district of the Japanese city of Osaka on Friday, the local fire department said.

TV footage showed dozens of firefighters working inside and outside the eight-storey building after the blaze was extinguished.

The charred interior of the fourth floor of the narrow office building was visible through broken and blackened windows.

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The floor housed a clinic that provided mental health services and general medical care, local media said.

An Osaka fire department official told AFP no signs of life could be detected in 27 of the 28 people injured in the blaze, with the victims being taken to hospital.

"The fire was detected at 10:18 am at the fourth floor," they said. "As of noon, 70 fire engines are at the scene."

The blaze, in the busy business area near Kitashinchi train station in the city in western Japan, had been put out after half an hour, the official said.

A middle-aged woman who witnessed the fire told public broadcaster NHK: "There was lots of a dark smoke... there was a very strong smell, too."