One person was free and the second person was in the process of being removed just after 2pm, fire services said.
A rescue helicopter was sent by St John ambulance to attend the scene after they received a call about the accident around 1.30pm.
No one on board the bus appeared to be injured, including the driver.
The Police Serious Crash Unit were at the scene and have begun an investigation in to the cause of the crash.
The crash site section of the road is likely to remain closed for several hours.
Diversions are in place at:
• Hopkins Rd & Hinuera Rd
• Hinuera Rd & Firth Rd
• Puketutu Rd & Matai Rd