Man charged after allegedly carrying ‘gun’ on Sydney train

Police have swooped on a Sydney train station and arrested a man after receiving multiple calls he was carrying a gun on board.

Police said the man got into an "interaction" with another passenger, allegedly lifted up his shift and showed a handgun at his waist.

"The passenger then moved away from the man and contacted police on his mobile phone," they said in a statement.

Polices said the man was then chased through six carriages.

Officers boarded a train at Town Hall railway station around midday and arrested the 42-year-old

Footage obtained by 9NEWS shows what appears to be a firearm sitting on the platform.

Police have since revealed it was a cap gun.

The man was taken to Day Street Police Station, where he was charged with intimidation, wilfully interfere with comfort and safety of passenger and possession of unauthorised pistol.

He has been remanded in custody and will appear in court later today.