A woman on a parked bus was left shaken when the vehicle rolled down a hill and crashed after its driver hopped off for a "comfort stop".
Emergency crews were called to Pembroke St, in Hamilton, after the bus crashed down a bank just after 8.30am.
The Orbiter bus ended up on Waikato Hospital grounds, narrowly missing the Percival Flats building, used by administration staff.
A spokeswoman for the Waikato Regional Council, which contracts Pavlovich Coachlines to operate its Orbiter buses, said they had spoken with the woman, who was the sole passenger at the time.
The spokeswoman said Pavlovich, as well as the police, were investigating. WorkSafe NZ was also looking into the accident.