Investigators in Tokyo are looking into the derailment of a train within the Nippori-Toneri Liner automated guideway transit system. The trains operate without crews.
The train came off the tracks while making an emergency stop near Toneri-koen Station. The stop was in response to an earthquake alert that was issued on Thursday night.
The transport ministry says an official at the operation control center pressed an emergency button upon receiving the quake alert on Thursday night. The five-car train had left the station. The first three cars derailed when the train stopped.
A subsequent investigation by the transport ministry and others found that the derailment occurred at a section where trains change courses.
Officials say a train can become temporarily unstable when it changes its course.
Two officials from the Japan Transport Safety Board have been dispatched to conduct a thorough examination and identify the cause of the accident.
A meeting of the Tokyo Metropolitan Government's task force was held on Friday. The head of the traffic bureau said it could take several days to restore power to the system.