Graphic video has emerged of a man being tasered by police on an inner-city Sydney bus.

The video, filmed by one of the passengers on board the 377 service on Anzac Parade in Moore Park about 2:30pm on Thursday, shows the man, dressed in an orange jacket, being confronted by police and then pulled off the bus.

NSW Police said officers were performing random breath testing at Moore Park when the bus driver signalled for assistance following an alleged assault.

Boarding the bus, one of the officers told the man: "Get off the bus, you're under arrest for assault."

The man then appears to hit the taser being held by the officer.

NSW Police confirmed a 37-year-old man was tasered after "allegedly assaulting a police officer".

A spokesperson for police said when boarding the bus, the two police officers were told the man had allegedly assaulted two passengers.

The man was arrested and taken to Surry Hills police station.