Tokyo, Sep 20 (IANS): A Japanese bullet train operator is investigating what caused two linked Shinkansen trains to uncouple while moving at high speed, public broadcaster NHK reported on Friday.

A coupler on the Tokyo-bound two-train service on the Tohoku Shinkansen line became unhinged while it was running between Furukawa and Sendai stations in the northeastern prefecture of Miyagi on Thursday morning, causing it to make an emergency stop and services on the line to be halted for hours, the report said, citing railway operator East Japan Railway.

The company, also known as JR East, said it was the first time its coupled Shinkansen trains had detached while in motion. However, no injuries were reported among some 320 people aboard and there were no derailments of the cars, Xinhua news agency reported, quoting NHK.

JR East said its investigation revealed that the trains were travelling at a speed of about 315 km per hour when the uncoupling occurred.

The coupler was designed to detach only when the trains slow down to a speed of 5 km per hour or below, JR East said.

JR East said the cause of the incident is being investigated, but no external abnormalities have been found on the coupler.

The company quoted the driver as saying emergency braking was suddenly applied and no unusual noise was heard or shaking felt shortly before the coupler became unhinged.

JR East is conducting emergency visual inspections of all its Shinkansen trains coupled with operations.

Following the uncoupling incident, 72 trains on the Tohoku, Yamagata, and Akita Shinkansen lines were cancelled and 35 were delayed, affecting roughly 45,000 passengers, according to JR East.