At least 24 people have been confirmed dead from a fire that broke out at clinic in Japan's Osaka prefecture, the police said, adding that they are investigating the incident as a suspected arson.

The fire broke out on Friday within a medical clinic, which provides psychosomatic and psychiatric treatments, on the fourth floor of a building in Osaka's Kitashinchi district, reports Xinhua news agency.

After receiving a report of fire at around 10.20 a.m. local time, the local fire department sent about 70 fire engines and ambulances to the scene.

The fire was extinguished by around 10.45 a.m. local time after burning across an area of approximately 25 square metres for about 30 minutes.

Previously, a total of 28 people were found injured from the fire, among whom 27 people including 17 men and 10 women were in cardiopulmonary arrest and showed no signs of life, according to firefighters.

As of now, at least 24 deaths have been confirmed by doctors at a hospital.

Most of the injured were rescued from the fourth floor of the eight-story multi-tenant building located near JR Osaka Station, while a woman in her 20s was brought out from the sixth floor of the building, according to the firefighters.

The Osaka police have begun investigating what might have started the fire since there was a suspicion of arson based on the situation at the scene.

There was a report that a "man lit fire" in the building in Kita Ward in the western Japanese city, local media reported, citing investigative sources.

The police were also informed that the fire had been started from liquid dispersed from a paper bag brought in by a man who appeared to be in his 60s.

There was a witness report that the suspect placed the bag near the clinic's reception counter.

"I saw smoke coming out and there were a lot of fire trucks and ambulances. People were being rescued by a ladder truck. At one point, there was a power outage in the surrounding area," a witness working at a nearby restaurant said.

"When I looked outside, I saw an orange flame in the window on the fourth floor of the building," another witness working in a nearby office said.

"A woman was waving from the window on the sixth floor and seeking help."