Animation fans and Kyoto residents gathered at the site of Japan's worst mass killing in 18 years on Friday, offering flowers and prayers for the 33 people who died in an arson attack on an animation studio in the city.

A number of people gathered near the charred three-story studio of Kyoto Animation in the western Japanese city, where a day earlier a suspected arsonist shouted "Die!" and that he had been plagiarized before dousing the building with what appeared to be petrol and setting it ablaze.

On Friday morning people gathered in the rain at the edge of the cordon set up by police and fire officials.

"It's hard to put into words how I feel," said 27-year-old Yuichi Kumami, a self-described animation fan, who had taken time off work at his company in nearby Osaka to lay flowers at the site.

"They may not be able to produce the same kind of works again and it was my hope that there would be more memorable works in the future, but that may be impossible now and that is very saddening," he said, his voice cracking with emotion.

A pillar of Japanese popular culture, animation has become a major cultural export, winning fans around the world. Kyoto Animation has an outsized role in the industry, with its influence outstripping the list of works it has produced.

Local resident Kazuko Yoshida, 78, said she lived close to the site and had smelt smoke on Thursday. From her second-floor window, she saw smoke and helicopters.

"I wonder why the company was targeted, why those people had to be caught up in this. It sounds like the man who did it wanted to die," she said.

"If he wanted to die he should have died alone, why did he have to involve other people? He is a terrible person."

One 23-year-old university student paid his respects before going to his lessons. He said he was a fan of "anime", as Japanese animation is known.

"You hear about gun killings overseas, but anyone can get their hands on gasoline and that is pretty frightening," he said. "You can't stop people from buying gasoline, perhaps there's a way to offer help to people who might be tempted to commit crimes."

One local man, 82, passing by on his bicycle said he previously lived in the neighborhood.

"There was no fire escape on the outside of the building and I think that was a big reason why so many people died," he said.

"There was only one way for them to escape."