Firefighters Scott Allan, of Bluff, and Zac Ryan, of Alexandra, were on their way to a firefighters competition in Mosgiel when they saw a bus, with 32 passengers aboard, on fire about 100m from the Southern Motorway in Quarry Rd.
The pair pulled over to help.
They used two fire extinguishers to control the fire before the Mosgiel Station crew arrived and took over.
Mr Allan said he "just naturally did what you do being a firefighter".
However, it was a mystery man who showed up with the fire extinguishers in time who needed to be thanked, he said.
"I couldn’t have done what I done if it wasn’t for the young fella who dropped the extinguishers off.
"[He] turned up and he goes ‘you might want these’ and then he buggered off just as fast as he turned up."
The back of the bus was left completely charred but passengers said it could have been much worse if the mystery man had not dropped off the fire extinguishers in time.
The bus had been chartered by the Dunedin Gardening Club, who were beginning their year with a trip to the Lavender Row in Mosgiel.
Club president Midge Ruka said all of a sudden the alarm went off and the driver pulled over.
She and the driver knew exactly what to do because they had been doing these trips together for 20 years, she said.
Together, they got everyone off the bus safely.
However, danger was not averted because the bus was smoking and an explosion resulted in a ball of fire coming out of the back, Ms Ruka said.
Staff at the Z Station near Quarry Rd told her a man in a red Ford Falcon had taken the fire extinguishers without saying a word, she said.
It would have been a different story without the young mystery man’s actions and she wanted to get in touch and say thank you, Ms Ruka said.
