Hectic punch-up on Melbourne train after bike row

A man has sparked a riotous brawl on a Melbourne train after taking issue with a group of youths who'd brought their bikes onto the Metro.

Footage of the incident posted to Instagram by an onlooker has attracted the attention of media, police and transport officials since it was posted.

Video of the fight shows it started when an older man reacted angrily to the safety hazard presented by the group of young cyclists, who'd all brought their bikes onto the train.

"So what happens if the train has to hit the brakes real f**kin' quick? That bike goes flying," he said.

"What do you do about that? You hangin' on to it, are ya? Hey, next stop, get the f**kers off the train."

"F**k off mate, f**k off!" one of the boys replies, before getting up and approaching the man in an aggressive manner.

The man, expecting violence, decides to strike first and launches a fist at the face of the young man, which in turn sparks an all-out brawl.

The aftermath of the fight shows the middle-aged man calling those who brought the bikes onto the train "disrespectful f**king people".

In a statement provided to media, a Metro spokesperson said while incidents like the one in the video are rare, the behaviour is "disgraceful and unacceptable".

"We urge anyone that witnesses dangerous, illegal or anti-social behaviour to report the incident by pressing the emergency button in trains and on platforms or by contacting 000," they said.

"Our authorised officers work across the network as well as a dedicated security and surveillance team who investigate every reported incident in collaboration with Victoria Police."

Victoria Police say they are aware of the incident.