A man suspected of torching an animation studio in Japan shouted that he had been plagiarised and appeared to have planned the attack, media reports say after a blaze killed 33 people in Japan's worst mass killing in 18 years.
The 41-year-old man 'seemed to be discontented, he seemed to get angry, shouting something about how he had been plagiarised', a woman who saw the suspect being detained told reporters.
The unidentified man shouted 'Die!' before dousing the entrance to Kyoto Animation headquarters with what appeared to be petrol and setting it ablaze around 10.30am on Thursday, media reported.
The explosive blaze killed 33 people and another 10 people were in critical condition, authorities said late on Thursday, in Japan's worst mass killing since a suspected arson attack in Tokyo killed 44 people in 2001.
'I imagine many of the people who died were in their twenties,' said 71-year-old Kozo Tsujii, fighting back tears after laying flowers near the studio in the rain on Friday morning. He said he drives by the studio on his daily commute.
'I'm just very, very sad that these people who are so much younger than me passed away so prematurely,' he said.
Police searched through the smouldering shell of the building for clues on Friday.
A man resembling the suspect went to a petrol station on Thursday with two 20-litre cans, Japanese media said.
Two cans, a rucksack and a trolley were found near the site, and television footage showed what appeared to be five long knives laid out by police as possible evidence on the ground outside the three-storey building.
The suspect had no connection with Kyoto Animation and his driver's licence listed an address in Saitama, a northern suburb of Tokyo, public broadcaster NHK said. Little else was known about the man, who is under police supervision with serious burns to the face and legs, media reports said.
NHK showed footage of what it said appeared to be the suspect lying on his back on the ground as he spoke to a police officer, shoeless and with what appeared to be burns on his right leg below the knee.
Kyoto Animation, located in a quiet suburb about 20 minutes by train from the centre of Japan's ancient capital, produces popular 'anime' series such as the 'Sound! Euphonium'.
Its 'Free! Road to the World - The Dream' movie is due for release this month.
© AAP 2019