A passenger attempted to start a fire on a moving bullet train in southern Japan on Monday morning, just hours after a separate incident in which a man threatened another person on a train in Tokyo with an awl.
The incidents come just a week after Japanese authorities warned of "copycat" attacks following a rampage by a man dressed as The Joker, who stabbed random passengers and attempted to set fire to a train in Tokyo.
Kiyoshi Miyake of Fukuoka City was arrested on suspicion of arson at about 8.30am on Monday after allegedly starting a fire on a train travelling between Kumamoto and Shin-Yatsuhiro stations on the island of Kyushu.
The 69-year-old reportedly told police that he poured flammable liquid on the floor of the carriage, lit a strip of paper with a lighter and threw it into the aisle.
Local media quoted him as saying that he had "wanted to imitate" the attack on a Keio Line train in Tokyo on Oct 31 that left 17 people needing medical treatment for knife wounds or smoke inhalation.
Police were ordered to step up patrols in and around railway stations in the wake of the Halloween attack, which saw a man dressed as comic book supervillain the Joker attack fellow passengers with a knife before setting a train carriage alight.
Kyota Hattori, who was arrested at the scene, reportedly told police at the time that he "wanted to die" and carried out the attack on Oct 31 so that he would be sentenced to death.
The 24-year-old said he was inspired by a similar incident in August in which 10 people were injured in a knife attack on a Tokyo commuter train.
Kayoko Nakadai, a mother of two children who both take trains to senior high schools in west Tokyo every day, said the recent spate of attacks was "really worrying."
"I know that some people are stressed and having work or money problems, but is trying to kill a person the answer?" she asked. "It's really frightening to think that someone [who thinks like this] could be on a train at any time and there is no way to know."
"It's unbelievable that anyone could be killed for no reason."
Asked whether she thought the latest incident on a bullet train would lead to more copycat cases, she said, "I hope not, but it has been on the news all day so it could make someone else do something similar."
Chief Cabinet Secretary Hirokazu Matsuno said last week that police had been instructed to increase their presence at stations in the wake of the "brutal and malicious" attack on Oct 31, with railway operators told to step up security patrols to prevent copycats.
Social media users responded to the incident by calling for more surveillance cameras, plain-clothes police officers and the introduction of passenger checks before boarding trains.
Others said passengers could do more to be aware of their surroundings on trains by not using their mobile phones or listening to music.
In a separate incident, a subway passenger was arrested in western Tokyo on Saturday for threatening the people around him with a sharp hand tool.
The man, who has not been named, reportedly confessed to "menacing" other passengers but his actions have not been linked to the Halloween train attack.
Some social media users said media coverage of the cases might be encouraging more people to carry out similar attacks.
A post on the Yahoo Japan news site said: "Coverage of the Keio Line case was sensational and I believe that over-reporting in the media is one of the causes of these copycat cases."
Another poster — who claimed to be "scared to get on a train or bus" — asked, "Are they deliberately reporting the details to make it easier for other people to do the same?"
This article was first published in South China Morning Post.