AN argument over an oBike on a Melbourne train descended into chaos when two men started brawling in the carriage, to the shock of horrified onlookers.

A video filmed by witness Luke Bennie shows one man speaking aggressively to users of the controversial share scheme, who were sitting down with their bicycles.

The argument escalates when one cyclist flung his oBike on the ground and approaches the man, who subsequently swings a fist at his face.

The men threw punches in the carriage, to the shock of onlookers. Picture: Instagram
The men threw punches in the carriage, to the shock of onlookers. Picture: Instagram

Horrified onlookers then spring to their feet in an attempt to break the brawling duo up.

"Disrespectful f---ing people," the man shouts once the brawl dissipates.

Victoria Police was not able to determine if any statements were made because of the unknown date and time of the incident.

The footage was posted on Saturday and by Sunday afternoon had attracted 5500 views on Instagram.

Metro spokeswoman Sammie Black said the company was investigating the incident.

"While incidents like this are rare, the behaviour depicted in this video is disgraceful and unacceptable," she said.

"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 triple-0."

oBikes launched in Adelaide in October following a successful trial.

Last month, Lord Mayor Martin Haese said he would seek "very strong assurances that Adelaide will not be littered with bicycles".

"We certainly do not want to see a repeat of some of the incidences that have played out interstate," he said.

"We are going to be having a trial with one company. We would want to see that they have the operational protocols in place to manage bike litter.

"I fully expect us to be very strict about the enforcement of it."