Cheung, 51, and Hui, 25, were arrested for fighting in public areas. Both have been released on police bail pending further investigation.

One accidentally "bumped" into the other as their train approached Sham Shui Po station at around 5pm on Saturday, reports at the scene said.

The duo began to argue, and this escalated into a physical fight. Both got off the train and continued kicking and punching as they took an escalator to the concourse.

A video of the fight went viral online, showing Hui lunging forward and punching Cheung's face while the latter punched back.

Cheering "fight, fight" and filming with their phones, passers-by stood around the two men but no one tried to stop them.

Hui had dropped his phone before grabbing Cheung's collar and pushing him into a corner. An MTR officer then separated the duo, saying: "Sir, don't fight. Don't fight."

Police officers arrived at the station afterwards and arrested the two for fighting in a public area.

Both were sent to a hospital, as Cheung had sustained injuries to his mouth and waist while Hui felt unwell.

In the comment section under the video, netizens said the duo fought like MMA fighters, with one being on the "defensive" and the other "offensive." Some netizens even analyzed their fighting "tactics."

Others blamed the sweltering heat for the fight.

Last month, a street fight turned deadly when a 63-year-old man died.

On June 25, retiree Fung celebrated his birthday with six friends in a Tin Shui Wai restaurant.

After dinner, Fung and his friend, 61-year-old cleaner Pang Yuk-ting began to argue, which escalated into a physical fight. Fung sustained heavy internal bleeding in the brain and died on June 28.

Pang has been charged with one count of manslaughter. He is in remand until the next court appearance on August 18.