Flames leapt up the rear of the National Express bus in Quarry Bank to the alarm of motorists and passers by.
Crews from Haden Cross and Brierley Hill fire stations were called to the town's High Street at around 7am today.
They found around 20 per cent of the bus engulfed in flames towards the rear on the lower deck.
Two firefighters wearing breathing apparatus tackled the blaze on the 141 bus which goes through Halesowen, Old Hill, Cradley Heath and onto Merry Hill shopping centre.
National Express spokesman Jack Kelly said: "We can confirm that an incident involving one of our vehicles took place in Quarry Bank this morning.
"Nobody was hurt during the incident and we are working hard to establish the cause."
Crews left the scene at around 8.40am.