SHANGHAI - The Ministry of Railways has ordered a probe into the death of an off-duty rail worker who was killed during a fight on a train.

The victim, who has not been identified, died on Sunday after allegedly being beaten by three attendants working on the K256 service from Shenzhen to Hefei.

The captain of the train and another train staff member involved in the fight have been put under criminal detention.

Witnesses said the man was attacked during a quarrel that erupted when the train stopped at a station in Ganzhou, Jiangxi province.

On Tuesday, the ministry ordered bureaus in Shanghai and Jiangxi to investigate the incident and severely punish those responsible in accordance with the law.

According to an official news release, the victim had been commuting to work on the train when a fellow passenger, also an off-duty rail worker, began arguing with carriage attendants at about 10:45 pm.

The disagreement was over a card that is supposed to allow rail workers to travel by train for free, said the release.

About 20 passengers witnessed the fight, most of whom handed in written material with their fingerprints to show they are willing to talk about what they saw, according to a news report by Jiangxi TV.

Eyewitness Lai Lifang said the victim, who he described as middle-aged, was trying to stop the argument when he was attacked.

"A member of the train's staff who sells beverages and arrived during the quarrel grabbed the victim by his neck and started beating him. He punched him in the temple," he said.

Altogether three men, including two men in railway uniforms, were involved in the attack, said Lai, who added one was wearing a badge that read "captain".

Some reports say the victim was taken to a hospital at about midnight, where he died from severe injuries. However, a clerk at a Ganzhou first aid station said he was already dead when the ambulance arrived.

A worker at the Shanghai railway bureau's information office declined to comment, saying only that the matter is under investigation.

Qiu Yue contributed to this story.