NHK has learned that a man suspected of starting a deadly fire at a clinic in Osaka City, western Japan, appears to have blocked its exit to stop people from escaping.

Police say Tanimoto Morio is suspected of setting fire to the clinic on the fourth floor of an eight-story building on Friday. Twenty-four people were killed.

Police say they are investigating the 61-year-old man on suspicion of arson and murder, but have yet to seek an arrest warrant as he remains in serious condition at a hospital.

Investigators say security camera footage shows the man placing a paper bag on the floor of the clinic before kicking it over. The liquid that leaked from the bag then catches fire.

Investigators add the video also shows the man standing at the exit with his arms stretched out after the fire started.