A Sydney bus driver has been sprayed in the face at least six times with what’s believed to be capsicum spray in an attack described by police as “despicable”.

A State Transit Authority bus was being driven along Oxford Street in Sydney’s inner east about 10.30pm on Thursday when the driver stopped and told a man waiting at the bus stop he could not get on because it was full.

The man, who sat on the dash of the bus, began to abuse the 38-year-old driver before spraying him in the face with a chemical, suspected to be capsicum spray, and fleeing the scene, police said.

Detective Superintendent Gavin Wood said the man sprayed the bus driver in the face at least six times which resulted in the driver becoming incapacitated.

The 38-year-old began having trouble breathing and was treated at the scene by paramedics.

“It is despicable behaviour obviously by a coward,” Det Supt Wood told reporters in Sydney on Friday.

“The male bus driver was out working hard, working for the community, driving a bus full of commuters and for that, he’s attacked.”

The spray is being examined with Det Supt Wood saying the symptoms the driver experienced were similar to those experienced with capsicum spray.

Police are appealing for public information to help identify the attacker.

He is described as having short brown hair and at the time was wearing a blue long-sleeved business shirt with white dots, navy trousers and was carrying a satchel-style bag. The man spoke with an English accent.

“You need to come forward, it’s very clear from the footage, members of the community will know who you are,” Det Supt Wood said.

“Let your conscience be clear, don’t wait for a knock on the door from us, come forward.”

State Transit head of safety Wayne Potter said the 38-year-old man is in shock after the incident but is in good shape and is back at work.

He said there has been an escalation in anti-social behaviour on buses which “needs to stop”.

“This sort of behaviour is just outrageous,” he told reporters on Friday.

NSW Police Minister Troy Grant said it was “unacceptable behaviour” and urged the man to hand himself in to police.

-AAP