A crack and oil leak have been found underneath a running shinkansen bullet train in the first "serious incident" affecting the Japanese high-speed train system since the transport ministry's accident investigation commission was launched in 2001.

Believing that the trouble could have led to a high-speed derailment, the Japan Transport Safety Board on Wednesday conducted a hearing with officials of West Japan Railway Co., operator of the troubled bullet train, among others.

According to JR West, the crew of the Nozomi No. 34 bound for Tokyo noticed on Monday afternoon a burning smell when the train left Kokura Station in the southwestern Japan prefecture of Fukuoka.

Although maintenance crew boarded the shinkansen at Okayama Station and heard an abnormal motor sound, JR West judged it would not affect the operation of the train and continued the run.

However, as the bullet train left Kyoto Station an abnormal smell was detected again and JR West checked underneath the train at Nagoya Station and found an oil leak.

The operator halted the service and some 1,000 passengers changed to other trains, JR West said.

The company said a crack was found on the steel frame of the fourth carriage of the 16-car bullet train, which began its run at Fukuoka's Hakata Station.

JR West said the company did not find any abnormality when it conducted a sight inspection of the train on Sunday. It also conducted checkups on the motors of the bullet train at a carriage base on Nov. 30 but found no irregularities.

Prior to this, JR West had conducted a more thorough inspection in February this year when it separated the chassis and wheels of all the train's cars and also disassembled parts.

The safety board of the Ministry of Land, Infrastructure, Transport and Tourism said that if the frame of the carriage had broken, the wheel shafts would have been affected and the train could have derailed.

The bullet train car belonged to JR West's N700 series.

Central Japan Railway Co., the operator of shinkansen services between Tokyo and Shin-Osaka, said it plans to move the troubled train, now at Nagoya Station, to a nearby carriage base and conduct a joint inspection with JR West after the safety board completes its probe.

JR West operates bullet trains between Shin-Osaka in western Japan and Hakata.