The bus and car collided on the intersection of Stuart and Smith Sts just before 4pm.
Geena Fagan witnessed the crash and said the bus - the number 51 GoBus - was travelling up Stuart St and failed to stop at a red traffic light.
A car travelling through the intersection on Smith St was hit by the bus, she said.
Nearly 20 people, mostly school children, were taken off the bus after the crash.
St John spokesman Ian Henderson said an ambulance attended but no-one was injured.
GoBus operations director Nigel Piper declined to comment on the cause of the accident, as it was under investigation by police.
''GoBus will be co-operating fully with the investigation. The welfare of those involved is our main concern at this time and are thankful that no-one was seriously injured.''
A police spokeswoman said inquiries were continuing.
