East Japan Railway is investigating the decoupling of two Shinkansen bullet trains running in Tokyo on Thursday morning.



The linked Hayabusa and Komachi trains on the Tohoku Shinkansen line became separated at around 11:30 a.m. while traveling between Ueno and Omiya stations in Tokyo and Saitama Prefecture.



The decoupling caused an automatic brake to activate and the trains came to a stop on the tracks.



JR East says the trains had been traveling at about 60 kilometers per hour and that after separating were about eight meters apart.



There were 642 passengers on the trains, but no one was injured. All of the passengers got off at Omiya Station.



Shinkansen service on the Tohoku and other lines was disrupted for about three hours.



A similar decoupling took place on the line in September last year.



JR East says it took preventive measures after that incident, so a different mechanical malfunction may have been involved in Thursday's case.



The operator says the trouble was very likely caused by a malfunction of an electrical system related to the coupling mechanism on the Komachi train.



The firm says it will suspend all coupled Shinkansen operations until the cause is identified and preventive measures are put in place.



This means that some direct Shinkansen services to Akita and Yamagata will be suspended.



Passengers going to Akita will have to change trains at Morioka Station, and those to Yamagata at Fukushima Station.



The government's Transport Safety Board says it will investigate the case as a serious incident that could have led to a major accident.