A car roared into a crowd of spectators at a drift event in Saga Prefecture on Sunday, leaving four men injured, including one in critical condition, police said.
A man in his 40s was unconscious after suffering a traumatic brain injury and a man in his 20s had a broken jaw, while the driver in his 20s hurt his neck and a man in his 30s in the passenger seat sustained a chest injury.
About 100 people were watching the event in the ski resort parking lot in the town of Fuji when the accident happened.
The police are investigating whether proper safety measures were in place. The event was organized by a local auto sales and repair company, Carpit Morinaga.
Junpei Morinaga, president of the company, said he felt a sense of responsibility and never thought such an accident could occur.
The injured spectators are all from Saga Prefecture. The two men in the car hail from Nagasaki Prefecture.
A total of 66 vehicles took part in the event showcasing rear sliding driving techniques. Japan is the birthplace of drifting as a sport.
The first international drifting competition endorsed by the International Automobile Federation was held in late September and early October in Japan.
At a motor sport circuit in Utsunomiya, Tochigi Prefecture, a 35-year-old woman was seriously injured during a drifting competition last year after a wheel of a car came off and hit her during a practice session.
She later died in a hospital.