A 29-year-old Brisbane City Council bus driver has been killed after a passenger allegedly doused him with a flammable liquid and set him alight.
Queensland Police Superintendent Jim Keogh said the bus, carrying six passengers, pulled into Moorvale Shopping Centre on Beaudesert Road to pick up three passengers.
Terrorism has been ruled out as a motive at this stage, he said.
"At that time that one of the passengers entered onto the bus and poured a flammable liquid onto the driver and subsequently the driver was set alight and is now deceased," Superintendent Keogh said.
"The fire was substantial, he would have stood little chance.
"Our inquiries indicate it was a rather rapid, a lot of the finer details won't be known for some time."
Supertintendent Keogh said a 48-year-old man, who was located at the scene, was in custody.
"Police are speaking to passengers, as you can imagine they are traumatised, we are providing assistance in that regard," he said.
"They are visibly shaken, traumatised."
Superintendent Keogh said it was a senseless and confronting act.
"I have been confronted with many situations but this is a rare one, but this is a rare one with no apparent motive, we are not alleging a robbery," he said.
"It is a senseless, needless taking of a young life of a person who was supporting the community by providing public transport."
Superintendent Keogh said "words escaped him" in terms of how shocking the incident was.
"It is a horrific incident here in the quiet suburb of Moorooka," he said.
"A bus driver going about doing his business, supporting the community and has taken his life from him in a senseless and needless act."
A bystander was labelled a hero after he kicked out the back door of the bus to allow passengers to escape.
"I just said to him 'you just saved people's lives'," onlooker Clair Savage said.
She said the man, who quickly left the scene, had run out of a nearby shop within 20 seconds of the fire.
Ms Savage described seeing a "gigantic set of flames" at the front of the vehicle.
Another onlooker, Julie Meadley, said she arrived just after the fire broke out and saw a mother and child banging on the door.
"It filled with smoke and they couldn't get out, " she said.
"People, onlookers, pried open the doors to get them out."
Emergency services were called to Beaudesert Road about 9am Friday morning.
The Queensland Ambulance Service said 11 were treated at the scene, some with minor injuries and some who were taken to hospital.
Queensland fire and emergency services had the fire under control at 9.19am and completely extinguished it one minute later.
The firefighters then conducted a search of the vehicle and passengers were being treated by the QAS.
A spokeswoman for Lord Mayor Graham Quirk said he would offer some public statements later on Friday.