Police are investigating after a woman threatened to stab a man with a chisel on board a Sydney train after the victim sat next to her.

The shocking Boxing Day altercation was caught on a mobile phone camera and shows the woman advancing on the man screaming “I’ll stab you, dog” as she brandishes the chisel.

The incident was only headed off when another passenger intervened, tackling the woman onto a seat and disarming her.

Witnesses said the dispute started as the train pulled out of Canterbury station about noon, in Sydney’s south west.

The woman, who was sitting in a window seat, objected to the man sitting two seats away from her, on the aisle.

“Move,” the woman, wearing a hooded pink jumper, yells, only for the man to turn on her and swear.

The pair begin to argue, with both accusing the other of touching each other.

“Move, you pig,” the woman tells the man, before walking down the aisle – only to suddenly turn around and brandish the chisel.

She repeatedly waves the blade at the man and dares him to come closer.

Another passenger eventually broke up the fight, pushing the armed woman onto the seat and holding her by the wrist before telling her to leave the train.

Ashfield Local Area Command is now investigating the incident, a NSW Police Force spokeswoman said.

“We’re still appealing for anyone with any information to come forward,” she said.

A Sydney Trains spokesman said the organisation was aware of the incident.