The discovery of a 16cm long crack in a Japanese bullet train coach could have led to a major accident, a West Japan Railway official said on Wednesday.
West Japan Railway President Tatsuo Kijima told Efe news that the incident was unacceptable and they were aware of its seriousness.
The crack was discovered in the undercarriage of the train on December 11 when the crew noticed a burning smell and unusual motor sounds.
The Tokyo-bound train was stopped at Nagoya, 350 km from the capital, and the crew inspected the 80 coaches and found problems in one.
The crack - the first serious incident in the high-speed train network since it was launched more than 50 years ago - was discovered in the steel frame that supported the set of wheels in the Nozomi 34 model train.
Kijima also regretted the fact that the train was not stopped immediately after the irregularities were noticed and said they were investigating the details of the incident to avoid a repeat.
Security has become a priority for the railway company after the derailment of a suburban train in 2005 which killed 106 passengers and the driver in the Hyogo prefecture.