Johannesburg - Authorities have confirmed that no one was injured when a Metrobus caught fire and exploded on Kingsway Avenue in Auckland Park, Johannesburg, on Tuesday evening.Emergency medical services spokesperson Robert Mulaudzi told News24 that the circumstances surrounding the explosion were still unclear, but that the fire may have been caused by a mechanical problem."We can confirm that a bus caught on fire about 30 minutes to an hour ago. There were no injuries and the fire has been contained," he said.Johannesburg Metro Police Department's Wayne Minnaar said that officers were at the scene to divert traffic.A witness, Giovanni Noel, 20, said he was on his way home when he saw a bus on fire."I was on the bus at the back, but not this bus. I jumped off the bus and I assisted traffic to try and clear up the road," he said."The bus was empty when it exploded, by the time I got there."Noel said the bus driver tried to douse the flames but had little luck as the blaze spread."I am grateful that everyone who was in the bus is alive. I hope they are alive."'It was freaky'A witness who asked to remain anonymous said she saw the driver of the bus running out of the bus with his passengers."There was another metro bus that was waiting for them, they got into that bus.""I looked out of the window and fortunately no one was inside of the bus. No one was injured. I got such a fright, for a bus to explode, it was freaky," said Lusizi.UJ students Theo Murimwa, 22, and Mvano Manyi, 20, also witnessed the incident.Manyi said: "At first we thought someone was getting shot but then we saw that the bus was on fire."We are just happy that no one got hurt, the driver got out last. What a good lad."Another witness who lives at Kingsway Place, Karabo Magano, 29, said he said he saw the smoke and thought it was a braai."I was standing at the top floor, and then we saw what was happening. As we saw it getting worse, my boys said it (the bus) was going to blow up," he said."I could feel the heat from up the building...I wondered where the people were, where was the driver."Magano said he could see fuel leaking from the bus.Attempts to reach Metrobus for comment were unsuccessful.