A Cairns woman who observed what she describes as a racist incident on a bus ride has sparked heated debate on social media.

The woman's post in a crime-related group on Facebook earlier this afternoon centres on a bus ride from Smithfield into the city in which indigenous people were allegedly abused and, in retaliation, the passenger responsible was allegedly assaulted.

Police confirmed to TropicNow this afternoon that officers were called to a disturbance on a Sunbus at Smithfield this morning.

The alleged victim did not make a complaint and police won't take further action.

This afternoon, Sunbus confirmed with TropicNow that an incident involving anti-social behaviour and an alleged assault occurred on a Cairns service about 10am.

"The bus driver immediately notified our operations centre and police swiftly arrived at the scene," genereal manager Sunbus Cairns Bob Osmond said.

"All Sunbus Cairns buses are equipped with CCTV cameras to monitor anti-social or unsafe behaviour. If passengers notice any such behaviour, we encourage them to report it to the driver as soon as possible."

Earlier, the Facebook post talks about the incident beginning shortly after four indigenous people got on the bus at Smithfield, sat at the back and were talking amongst themselves.

"Whilst on the bus to the city just a short time ago I just witnessed racial conflict at its worst," the post says.

"4 Aboriginal people got on at Smithfield... they sat at the back of the bus talking amongst themselves, granted they were a little noise but nothing too bad.

"Suddenly a lady in the middle of the bus started shouting "oh will u shut up" making comments like "I can't stand hearing "those people" talk, "their voice just annoys me" , all they do is talk talk, I can stand it" and just get these people off will you".

"OMG! Well lady, as much as I agree no one should ever be assaulted... You kinda had it coming... They were not hurting anyone... They were kicked off a bus for no reason."