A driver fell asleep for eight minutes at the controls of a Japanese bullet train travelling at almost 300 kilometres (186 miles) an hour.
The Japanese bullet train is renowned for its safety
The shinkansen ran for about 26 kilometres before an automatic control system kicked in, and it was brought to a halt, short of the platform at the next station at Okayama, east of Hiroshima. No-one was injured.
Officials sent to investigate found the driver still fast asleep in his cab, and said he did not wake up until shaken.
An inquiry has been launched into what is sure to be seen as at least an embarrassment, given the Japanese railway system's reputation for safety and punctuality.
The 33-year-old driver, who has not been named, said he had no memory of what had happened.
The train is believed to have been on automatic pilot at the time, although drivers normally take over the controls as they approach a station.
A spokesman for the West Japan Railway said the driver had had plenty of sleep, and had not been drinking alcohol.
"We are very shocked," said Kosuke Sugiyama of the company's public relations office. "Our business is all about passengers
trusting us enough to travel on our trains."
The driver has now been removed from driving duty, said the company. It is yet to decide whether he will return to the controls.