A supervisor at the company said there were passengers on the bus when the man was stabbed but did not know exactly what had happened.
Counties Manukau District Command Centre acting Senior Sergeant Steve Meade said quick work by police helped prevent the injuries becoming more serious.
Passengers on the bus were being spoken to and will be offered support, he said.
A 15-year-old and a 20-year-old arrested this evening at a nearby address will appear in the Manukau Youth Court and District Court tomorrow.
Police are continuing to investigate the attack.