Some 82 trains running on the JR Chuo Line were canceled Monday morning because the roadbed on a section running through the Namikicho area of Hachioji, western Tokyo, was found to have fallen away, according to East Japan Railway Co.
An estimated 31,000 people traveling between Hachioji and Takao stations were affected as 82 trains scheduled to run in the early morning hours were canceled or delayed, company officials said.
No one was hurt as a result of the collapse, which was discovered at around 3 a.m., and services on the line were restored to normal around 9:30 a.m., they said.
Engineers making regular rounds of the track found the section of roadbed had subsided, leaving a hole roughly 70 cm wide close to a grade crossing, the company officials said.
They said the current construction of a tunnel as part of a 16-meter-wide city road under the collapsed section may have caused the cave-in.
The construction of the tunnel was begun by JR East in November 1995, and the erection of a concrete box 16 meters square and 7 meters high, which served as part of the tunnel's main frame, was almost complete when the cave-in occurred, according to the carrier.
Officials at the firm said they suspect the roadbed caved in because earth and sand had flowed into gaps between the concrete box and pipes buried next to it -- which were used to to shore up the bank under the track bed -- adding they were investigating to pinpoint the exact cause.
The tunnel was to be completed in July, and the construction of the city road was to be finished by the end of next year, they said.