There were no passengers on board and the driver was left shaken but escaped without injury. Police are waiting to get full details from him.
Sgt Andy Kneen said: "We are still trying to establish what happened. Luckily no-one was injured."
The police received numerous 999 calls from pedestrians nearby.
Sgt Kneen added: "We have an officer from the road policing unit who is investigating the incident and we have people working on this from PSV, the Manx electricity authority to make sure there are no electrical problems.
"As I understand it the bus was travelling down Prospect Hill but we haven't had a chance to speak to the driver properly.
"He was shocked but unhurt and has been very helpful and cooperative." BBC