The two men were taking a Sheung Shui bound East Rail train on Christmas Day. The 43-year-old took off his mask as he feasted on siu mai and fish balls, while the older passenger asked him not to do so.

The quarrel escalated into a fight, and the younger man used his mobile phone to hit the older passenger in the head. A piece of siu mai fell and its sauce spilled onto the floor.

According to a video circulating online, blood oozed from the 63-year-old's head as other passengers shouted "stop fighting" repeatedly.

When MTR staffers arrived at the scene, the older man explained that he wanted the other man to put his mask back on. The 43-year-old yelled at onlookers, asking them not to make a fuss. He told the staffers he fought with the other man, and the two were taken away at Kowloon Tong MTR station.

Netizens criticized the younger man for breaching MTR rules by eating on the carriage, ignoring advice, and beating the other person instead.

Some were not convinced that it was a "fight" involving two parties and said it appeared that the younger man simply unleashed his rage on the older passenger in an act of violence.