AS BLACK smoke rose from the floor of a Sydney L94 bus yesterday morning , passengers yelled out for the driver to stop: ''Hey mate, your bus is on fire.''
Greg Pallier, who was sitting in the back seat, said the driver quickly pulled over near the corner of Oxford and Flinders streets, Darlinghurst, at 9.30 and about 30 passengers piled out.
Mr Pallier called triple-0 and watched as flames leapt over the bus's roof.
''As the smoke was getting thicker, a couple of guys came out of a pizza shop on the corner and used two fire extinguishers on the bus. But the fire just got bigger and bigger,'' he said.
The Office of Transport Safety Investigations was looking into the cause of the fire that left the engine door of the diesel-powered 1993 Scania bus badly charred, the back window shattered and plastic signage peeling off.
''It's far too early at this stage to identify a particular cause,'' the deputy chief investigator John Hartmann said, adding there would be a routine check of its maintenance records.
Investigators were expected to brief the office about their findings into a potential cause of the fire today.
Mr Pallier, who catches the L94 from Kingsford to his city office most days, said most of the passengers were fairly calm as they scrambled off.
''When we got off the bus you could see flames all over the ground,'' he said. ''It was a pretty hot fire. It got really hot really quickly.'' But another passenger, Faridah Merchant, said she was scared as the inside of the bus grew ''very, very hot'', and noticed a few people were starting to panic.
''I've never been in such a situation in my life. You don't think it's ever going to happen to you,'' she said. ''I was very shaken. I'm OK now, but I'm still in shock. I'm kind of put off ever going on a bus after this.''
Last October, an explosion on a gas-powered State Transit bus triggered snap industrial action, when the union representing bus drivers instructed them to take them out of service.
''I would say that there's no history with that particular [diesel-powered] model bus catching on fire,'' the Rail Tram and Bus Union bus and tram division secretary, Chris Preston, said. ''I think it might be just one of those things.''