A bus driver was killed in a "senseless" attack after a passenger threw an "incendiary device" at him and he was burned alive.
The shocking incident happened just after 9am local time in the south Brisbane suburb of Moorooka.
A 48-year-old entered the TransLink bus while it was stopped on Beaudesert Rd and threw "an incendiary device" at the driver that caused a fire, Queensland Police Commissioner Ian Stewart said on Friday afternoon.
It was initially thought the driver, Manmeet Sharma, 29, was doused in some sort of accelerant, but police now allege a device was thrown at the driver.
Stewart said counter-terrorism police had joined the inquiry, as a precaution, however there was no suggestion terrorism was a motive. There was also no evidence it was a racially-motivated attack.
Earlier on Friday, Queensland Superintendent Jim Keogh told reporters at the Moorooka scene "There is no apparent motive. We're not alleging robbery - this is the senseless, needless taking of a life going about supporting the community by providing transport."
The attack was not terrorism-related, but police were stunned by how sudden and brutal it was.
"It would appear random," they said.
Sharma is believed to be casual who had only worked for the company for a few months.
The alleged attacker was "compliant" with officers who arrested him. He was taken to hospital to be treated for minor burns and was on Friday afternoon being spoken to by Homicide detectives.
"The bus pulled in for the purpose of picking up passengers at the stop, there were six people on board at the time," Keogh said.
Asked if there was any suggestion the two men knew each other, Keogh said there was nothing to suggest a connection.
Supt Keogh said it was a "horrific incident" that had shattered the quiet suburb of Moorooka and "words escaped" him how awful it was.
Six "deeply traumatised" passengers have been taken to hospital to be assessed, mainly for minor injuries like smoke inhalation.
They were lucky to escape with their lives from the "substantial" fire. Some were already on the bus and others were at the bus stop where the arrested man had been waiting.
One woman was so upset she couldn't even talk to rescuers.
A taxi driver told The Courier Mail he busted down the back door of a bus to allow passengers to escape the inferno.
Aguek Nyok, a local cab driver who had stopped to get a haircut, said he saw the bus erupt into flames.
"Literally as I pulled up I saw and heard the front of the bus explode and a guy ran out and he was covered in flames, head to toe," he said.
"All the people were at the back trying to get out of the bus but they couldn't get out the front because of the flames."
Keogh said the driver's actions were "heroic at the very least" and he praised the response by others who tried desperately to help.
Other onlookers said they could hear terrified screams coming from the bus.
A shop owner tried to put the blaze out with a fire extinguisher but the fire kept starting again - and the driver was still trapped inside.
The fire was eventually extinguished by 10am.
The bomb squad left the scene after searching the bus for any suspicious objects. The bus will now be towed away for a full forensic examination.
A statement from the Queensland Bus Industry Council said today was a "sad day for all within Queensland's bus industry".
"To say we are shocked that such an event could occur so unexpectedly is an understatement. We are also thinking of those passengers who witnessed this action today and wish them the best as they deal with this traumatic experience."
All inbound lanes of Beaudesert Rd were closed, with detours in place.